The words the care guides use without explaining them. A dotted term on any guide opens its entry here.
Tank setup
Acclimation
Acclimation eases a new animal from bag water into tank water, so it takes the change in temperature, pH, hardness and salinity slowly. Float the sealed bag 15 to 30 minutes to match temperature, then add tank water in stages. Shrimp, marine fish, corals and wild-caught fish get a drip line instead, a few drops a second over one to two hours. They react badly to a jump in TDS or salinity. Net the animal into the tank and pour the bag water away. Ammonia builds in a bag during shipping, and opening it raises the pH and turns that ammonia toxic. A long open float on a shipped bag does more harm than good.
Water chemistry
Activated carbon
Activated carbon is a porous black media that dissolved compounds stick to as water passes through it. It clears tannins, the yellow tint of an old tank, medication left after a treatment and the smell of a coral war. It does nothing to ammonia, nitrite or nitrate, so it is not a substitute for a water change. A bag of it exhausts in two to four weeks and then sits there as mechanical media. Rinse it first, run it in flow rather than buried in a corner, and take it out before dosing any medication. Reef keepers run it in small amounts, since a large fresh batch strips a tank fast.
Equipment
Air pump
An air pump sits outside the tank and pushes air down a line to an airstone or a sponge filter. The bubbles themselves add almost no oxygen. What they do is drag water up to the surface, and the surface is where gas exchange happens. That makes an air pump useful in a heatwave, in a heavily stocked tank and during a filter outage. A sponge filter runs on one, which is why quarantine tanks, fry tanks and shrimp tanks use them. Fit a check valve above the water line, or a pump below the tank siphons water out when the power goes off. Bettas dislike the current a big airstone makes.
The trade
Albino
An albino animal cannot make melanin, the dark pigment, so it shows white, pink or yellow with red or pink eyes. Yellow and red pigments are unaffected. That is why an albino Corydoras aeneus is pale pink and an albino tiger barb is cream and orange. It is a recessive trait fixed into strains of corydoras, bristlenose plecos, danios, kribensis and Oscars. Albino fish see poorly in bright light, so they feed better under floating plants or a dimmed fixture. They are no more fragile than the base form otherwise.
Biology
Algae
Algae are simple plants that grow wherever there is light, water and a nutrient to use. Every tank grows some, and a thin green film on the back glass feeds otocinclus, nerite snails and shrimp. The named kinds behave differently. Diatoms are the brown dust of a new tank, hair algae comes with excess light, and cyanobacteria is a bacterium wearing the same look. Green water is algae in suspension rather than on a surface. An outbreak is a balance problem, not a cleaning problem. Cut the photoperiod to six or seven hours and feed less. Raise the water change volume, and add fast-growing stem plants to take the nutrients first.
Feeding
Algae wafer
An algae wafer is a hard sinking disc of spirulina and other vegetable matter, made for bottom feeders. Plecos, otocinclus, corydoras, snails and shrimp all work on one. It stays intact for hours, so a slow grazer that feeds after dark still gets a share. Drop one in at lights out for the nocturnal plecos. Feed one wafer per two or three fish and pull the leftovers in the morning, because a wafer left for days fouls the sand. A wafer is not a complete diet on its own. Wood-eating plecos still need driftwood, and otocinclus still need a mature tank with algae on the glass.
Water chemistry
Ammonia
Ammonia is the first waste product of fish, uneaten food and dying plants, and the most toxic of the three nitrogen readings. Anything above 0 ppm burns gills and damages fish. Bacteria in a cycled filter turn it into nitrite within hours, so an established tank reads 0 ppm even when fully stocked. A reading turns up in a new tank, after filter media is rinsed under the tap, or when a fish dies unnoticed. Warm, alkaline water makes it worse, because more of it is present as free ammonia rather than ammonium. The answer is a large water change and less food, not a bottle of chemicals.
Anatomy
Anal fin
The anal fin sits on the underside of a fish, between the vent and the tail. It works with the dorsal fin to keep the fish upright and stop it rolling. In guppies, mollies, platies and swordtails the male's anal fin is rolled into a narrow rod, the gonopodium. He uses it to pass sperm to the female. That rod is how you sex a livebearer at a glance: a fan-shaped anal fin is female, a rod is male. In many cichlids the anal fin carries the egg spots, the yellow ovals a male flashes during spawning.
The trade
Aquacultured
Aquacultured means grown on a farm or in a facility rather than taken whole from the reef. In corals it means a frag cut from a captive colony and grown on, which is where most hobby corals now come from. Maricultured is the middle case, a frag glued to a plug and grown out on a sea farm. Aquacultured corals arrive already used to aquarium light, flow and parameters, so they settle faster. They bring no hitchhiking pests beyond what the farm carries. In fish it overlaps with captive-bred and covers the clownfish, dottybacks, cardinalfish and gobies now raised in numbers.
Tank setup
Aquascape
An aquascape is the arrangement of hardscape, substrate and plants inside a tank. The named styles come from competition. Nature aquarium layouts use wood and stone in odd-numbered groups. Iwagumi uses stone alone over a carpet. Dutch tanks use blocks of stem plants and no wood, and a biotope copies one river or stream. A layout is a fish decision as well as a visual one. Broken sightlines let a chased fish get out of view, and open sand suits corydoras and eartheaters. Lay the hardscape out dry, take a photo, and change it before any water goes in.
Tank setup
Aquasoil
Aquasoil is baked, nutrient-loaded soil sold in granules for planted tanks. It holds nutrients at the roots, so carpets and crypts grow in it faster than in inert gravel. Most brands are acidic and soften the water, pulling a tap-water tank toward pH 6.5 and a lower GH. That suits shrimp and soft-water fish. New soil leaks ammonia for two to six weeks, so a soil tank is planted heavily and cycled before any fish go in. It loses that buffering after a year or two, and it turns to mud if it is dug up. Plan the layout before you plant, and top-dress rather than replace.
Tank setup
Aragonite
Aragonite is calcium carbonate in the form corals and shells build with, sold as reef sand and as crushed coral gravel. It dissolves slowly in water that has gone acidic, which puts carbonate and calcium back and lifts KH and GH. That makes it the substrate for reef tanks and for Rift lake cichlids. A handful in a filter bag holds a Malawi or a goldfish tank in hard water. It will not push the pH much past 8.2 on its own, because it stops dissolving once the water is alkaline. Soft-water tanks keep it out, since even a little raises hardness. Rinse it well, since fine aragonite clouds a tank for days.
Behavior
Aufwuchs
Aufwuchs is the furry mat of algae, diatoms and small invertebrates that grows on rock in sunlit water. It is the main food of Lake Malawi mbuna, several Tanganyikan cichlids and the plecos that graze stone. Those fish are built to rasp it rather than chase prey, and their long guts suit a vegetable diet. Feeding mbuna a rich meaty food brings on bloat. In a tank the mat is replaced by spirulina flake, algae wafers and blanched vegetables. Leave the algae on the back glass and the rockwork rather than scraping every surface clean.
Equipment
Auto top-off
An auto top-off replaces water lost to evaporation, using a sensor in the sump and a small pump in a reservoir. The salt stays behind when water evaporates, so a reef tank left alone for three days climbs in salinity. Topping up by hand once a day does the same job less steadily. Fill the reservoir with fresh RO water and never salt water. A stuck pump is the failure that matters, so run a second float switch as a backup. Keep the reservoir small enough that a full dump would not crash the salinity. Reefers who dose kalkwasser run it through the top-off, so the calcium goes in all day.
Anatomy
Barbels
Barbels are the whisker-like feelers around the mouth of catfish, loaches, many barbs and goatfish. They are covered in taste and touch receptors for finding food in sand, silt and dim water. They are why a corydoras can feed face-down in sand and a kuhli loach can hunt at night. They also report on the tank. Sharp gravel, a dirty substrate or a bacterial infection wears corydoras barbels back to stubs, and they regrow only on soft sand in clean water. Short barbels on a shop fish say how it was kept, not what species it is.
Tank setup
Bare bottom
A bare bottom tank runs with no substrate, so the glass is the floor. Waste sits in plain sight and a siphon takes it out in seconds. That is why quarantine tanks, discus growout tanks, fry tanks and breeding setups are usually bare. Medication dosed into a bare tank stays at the level you dosed, since there is no sand or gravel to soak it up. Some SPS reef keepers run bare bottom for the same reason, with high flow keeping detritus in suspension. The cost is looks and the loss of sand for corydoras and other sifters. A dark background or a painted base cuts the glare fish get off bare glass.
Behavior
Biofilm
Biofilm is the slippery layer of bacteria, algae and microscopic animals that coats glass, wood, leaves and substrate in any tank left running. Baby shrimp and many newly free-swimming fry eat nothing else for their first days. That is why a shrimp tank is matured for a month or two before the first shrimp go in. Leaf litter and cholla wood hold far more of it than bare glass. Biofilm is not dirt. Scrubbing every surface in a shrimp tank removes the food supply, so leave the back glass, the side glass and the hardscape alone.
Tank setup
Bioload
Bioload is the amount of waste the animals in a tank put out, counted as ammonia the filter has to process. It follows body mass and feeding rather than the number of fish. One 12 in (30 cm) oscar carries a bigger bioload than twenty neon tetras. Goldfish, plecos and most cichlids are heavy feeders and heavy producers. A tank over its bioload shows it as nitrate climbing fast between water changes, not as an ammonia reading. The filter usually keeps up long after the water quality has slipped. Match the bioload with more water changes, more filtration and fewer or smaller fish.
Water chemistry
Blackwater
Blackwater is water stained tea-brown by tannins from leaf litter and wood, very soft and acidic, with little light getting through. Blackwater rivers such as the Rio Negro run below pH 5 with almost no measurable hardness. Cardinal tetras, many dwarf cichlids and the wild bettas come from them. They color up and spawn in water that copies it. In a tank that means driftwood, leaf litter or other botanicals, dim light and soft water. The tannins tint the water and pull the pH down a little on their own. Blackwater is not dirty water. The stain is tannin, not waste, and the water underneath is usually very clean.
Feeding
Blackworms
Blackworms are live freshwater worms, usually California blackworms, sold as a wet clump in a tub. They stay alive in the tank and wriggle down into the sand, so a fish that ignores everything else will hunt them. Wild-caught fish, killifish and small loaches come around on blackworms when nothing else works. Keep the tub in the fridge and rinse the worms under cold water daily, or the clump turns to mush in a day or two. Feed a small pinch, since worms that burrow and die foul the sand. Tubifex is a different worm with a worse reputation, because it was collected from dirty water.
Marine
Bleaching
Bleaching is a coral pushing out the zooxanthellae that live in its tissue, so the white skeleton shows through. The algae supply most of a coral's food, and a bleached coral is alive but starving. Heat is the trigger on a reef. In a tank it is usually a new light run too bright too soon, a heater stuck on, or an alkalinity swing. A coral that bleaches can take its algae back over a few weeks if the cause goes away. Cut the light, hold the parameters steady and feed the tank lightly. A coral that stays white for a month is usually lost.
Feeding
Bloodworms
Bloodworms are the red larvae of midges, not worms at all, sold frozen in cubes, live in tubs or freeze-dried. The red comes from hemoglobin, which lets them live in low-oxygen mud. Nearly every fish that takes meaty food eats them, which makes them the standard way to get a shy or newly imported fish feeding. They are high in protein and low in almost everything else. Feed them two or three times a week rather than every day. Thaw frozen cubes in tank water and pour the pack juice off before feeding. Some keepers get an itchy rash from handling them.
Tank setup
Botanicals
Botanicals are dried leaves, seed pods and bark added to a tank on purpose. Catappa leaves, also sold as Indian almond leaves, are the common one. Oak and beech leaves, alder cones, casuarina cones and cholla wood go in too. They release tannins, tint the water and pull the pH down in soft water. As they break down over four to eight weeks they grow the biofilm that baby shrimp and fry graze. Betta and shrimp keepers use them for that and for the mild antifungal effect on eggs. Rinse them or pour boiling water over them first. Add a few at a time rather than a layer at once, and replace them as they soften.
Water chemistry
Brackish
Brackish water sits between fresh and marine, roughly 5 to 20 ppt of salt. It is the estuary, mangrove and river-mouth water that scats, monos, archerfish, figure eight puffers and bumblebee gobies come from. Mix it with marine salt rather than aquarium or table salt, and measure it with a refractometer. Low-end brackish around 1.005 specific gravity suits figure eights and many gobies. High-end brackish near 1.015 suits adult scats and monos, which move toward full seawater as they grow. Most plants fail in it, and Java fern, Anubias and mangroves are among the few that hold on.
TankBud rating
Breeding
On TankBud, breeding is how hard a species is to breed in a home tank, rated easy, medium, hard or no record. Easy covers fish that breed in a community tank without help, such as the livebearers, convicts and kribensis. Medium covers fish that want a separate tank, a trigger such as a cool water change, and fry food. Most cichlids, corydoras and many catfish sit there. Hard covers fish that need precise water, live food for the fry or a particular spawning setup. No record means there is no reliable published record of the species spawning in captivity. That is the case for many marine fish and wild-caught oddballs.
Feeding
Brine shrimp
Brine shrimp are Artemia, the salt-lake crustacean the hobby feeds at two sizes. Frozen adult brine shrimp are a staple for most community and marine fish, and the enriched kind carries more fat and vitamins. Baby brine shrimp are the newly hatched orange specks most fry are raised on. Stir a quarter teaspoon of cysts into a bottle of salt water at about 1.018 specific gravity. Run an airline into it and leave a light on. They hatch in 18 to 36 hours at 78°F (26°C). The yolk sac they hatch with is the food, and it runs out inside a day, so feed them the day they hatch. Rinse them in fresh water first. Fry fed twice a day on baby brine grow visibly faster.
Breeding
Brood care
Brood care is what a parent does after spawning: fanning the eggs, picking off the dead ones and herding the fry once they swim. Cichlids, many catfish and the bubble-nest builders all do it, while egg scatterers drop their eggs and leave. A pair with brood care guards a territory the size of half the tank. They drive off anything that comes near, including their own older fry. It also means the eggs can stay with the parents instead of being pulled, which is how most cichlid keepers raise a first batch. Discus go further and feed their fry on skin slime for the first two weeks.
Breeding
Bubble nest
A bubble nest is a raft of saliva-coated bubbles a male blows at the surface. He catches the fertilized eggs in it and guards them until the fry swim free. Bettas, most gouramis and paradise fish build them, usually under a floating leaf or a piece of plastic film taped to the glass. Breeding tanks keep still water and a low level so the nest holds together. A male blowing a nest in a shop tank or a lone betta tank is displaying, not calling a female over. After spawning the male tends the nest and the female is taken out. The fry hang in the bubbles two or three days before they swim.
Water chemistry
Buffer
A buffer is a dissolved compound that soaks up acid and holds the pH steady. Carbonates and bicarbonates do that job in an aquarium, and KH is the test that measures them. A tank with 4 dKH or more holds its pH between water changes. Under 2 dKH the pH can fall overnight as the fish and filter make acid. Crushed coral, aragonite sand and a Rift lake salt mix add buffer on purpose. Commercial pH adjusters move the number without adding buffer, so it bounces back within a day. Soft-water fish want little buffer, and Rift lake cichlids want plenty.
Plants
Bulb
A bulb is a swollen storage organ a plant grows from, holding the energy for a fast burst of leaves. Aponogeton, tiger lotus, crinum and the banana plant all grow from one. Set it on the substrate or half-bury it with the growing tip clear, because a bulb buried whole usually rots. Many take two to four weeks to sprout and a dud never does, which is why they are sold in multiples. Several go dormant after a few months. The leaves die back, the bulb rests, and it sprouts again. Lift a dormant bulb and store it damp and cool, or leave it in the substrate.
Water chemistry
Calcium
Calcium is the mineral that snails, shrimp and corals pull out of the water to build shells and skeletons. Hard tap water carries enough for a freshwater tank. A cuttlebone or a few crushed coral chips top it up in a soft-water snail tank. A reef tank uses it far faster. Stony corals sit at 380 to 450 ppm calcium, and a growing reef pulls that down in days. Magnesium keeps calcium and carbonate from falling out of solution, so reefers hold it near 1300 ppm and test it alongside. GH counts calcium and magnesium together, which is why a soft-water tank is short on both.
Water chemistry
Calcium reactor
A calcium reactor is a sealed chamber of aragonite media that CO2 dissolves on demand. The gas drops the water inside to about pH 6.5, and the media goes into solution as calcium and carbonate. The effluent drips back into the sump and carries both to the corals in balance. It suits a big stony coral load, where two part dosing would mean mixing gallons of solution a week. Setup costs more than any other method and running it costs less. It needs a CO2 cylinder, a regulator and a needle valve. The CO2 it adds can pull tank pH down, so a refugium on a reverse light cycle usually goes with it.
The trade
Captive-bred
Captive-bred fish are bred and raised in captivity rather than collected from the wild. They are brought up on prepared food, so they take flake and pellets from day one. They are used to tank temperature and lighting, and they carry fewer parasites and no cyanide damage. Almost every clownfish, livebearer, corydoras, betta and danio in a shop is captive-bred. They are usually hardier in the water the hobby can offer, and sometimes smaller or paler than wild stock. Tank-bred is the same claim from a shop rather than a breeder, and tank-raised sometimes means wild fry grown on in a facility.
Anatomy
Carapace
The carapace is the rigid plate covering the head and thorax of a crustacean. On a shrimp it is the section in front of the tail, and the female's saddle shows through it. It is made of chitin stiffened with calcium, and it does not grow. The animal sheds the whole thing and hardens a larger one over the next day or two. A soft shrimp hides until the new carapace sets. Calcium and a GH of 6 dGH or more are what it hardens with. A shrimp stuck half out of the old shell usually failed on minerals.
Biology
Carnivore
A carnivore lives on animal food, and a piscivore is the part of that group that hunts fish. Oscars, arowana, pike cichlids, lionfish, groupers and most puffers feed this way. The diet decides the stocking more than the temperament does. A piscivore swallows any tank mate that fits in its mouth, and the mouth is wider than it looks. Feed frozen and prepared food rather than feeder fish, since feeders carry disease and a diet of goldfish brings on fatty liver. Frozen mysis, krill, silversides and carnivore pellets cover most of them. Feed adults three or four times a week rather than daily.
Plants
Carpeting plant
A carpeting plant spreads sideways across the substrate instead of growing up. Dwarf hairgrass, Monte Carlo, dwarf baby tears and glossostigma are the ones scapers use. They spread by runners, so they go in as small portions an inch or two apart and are left to join up. Strong light is what keeps them flat, because under a weak light they stretch upward for it and the mat never closes. Most want CO2 to fill in within a couple of months. Dwarf sagittaria and Monte Carlo are the two that will carpet in a low-tech tank, slowly. Cut the mat back before it lifts off the substrate in sheets.
Anatomy
Caudal fin
The caudal fin is the tail fin and the main source of thrust. Its shape says how a fish lives. A deeply forked caudal belongs to an open-water swimmer such as a danio or a tang. A broad rounded one belongs to an ambush fish such as a betta. The caudal peduncle is the muscular stalk in front of it. It carries markings used to tell species apart, and the black spot of a black phantom tetra sits there. Columnaris often shows first as a pale saddle across it. Long-finned varieties carry a caudal the fish cannot swim well with, so they want still water.
Breeding
Cave spawner
A cave spawner is a fish that lays its eggs on the roof or the back wall of a hole. Kribs, apistogramma, bristlenose plecos and a lot of other catfish breed this way, and the parent holds the doorway against everything. The eggs are hidden, so the first sign of a spawn is usually a fish that will not leave one spot. Give them a cave with one narrow entrance the fish barely fits through. A coconut shell, a clay pot on its side or a length of PVC all work. Male bristlenose stay in with the eggs to fan them and keep the fry inside for a week after hatching.
Equipment
Chiller
A chiller is a refrigeration unit plumbed into a tank, with a pump pushing water through it. It is the answer when a room runs warmer than the stock wants. Hillstream loaches, white cloud mountain minnows and most goldfish want water under 72°F (22°C). Caridina shrimp sit at 68 to 74°F (20 to 23°C). A reef tank in a hot summer climbs past 84°F (29°C) and starts bleaching corals. Chillers are expensive and they heat the room they stand in. Try a clip fan blowing across the surface first, since evaporation alone drops a tank 2 to 4°F (1 to 2°C).
Behavior
Cleaner
A cleaner fish or shrimp eats parasites, mucus and dead tissue off other fish. It works a set spot on the reef that other fish visit and hold still at. The skunk cleaner shrimp is the one that works in a tank. It sets up on a rock, cleans most fish and takes leftovers between clients. The bluestreak cleaner wrasse is rated difficult here, because many never take prepared food and starve in a tank with too few fish to service. Freshwater has no true equivalent, and the Chinese algae eater sold as one rasps the slime coat off other fish as it ages.
Tank setup
Cleanup crew
A cleanup crew is the group of invertebrates stocked to graze algae, turn sand and eat what the fish miss. In a marine tank it is astrea and trochus snails, nassarius for the sand, hermit crabs and a skunk cleaner or peppermint shrimp. In freshwater it is nerite snails, amano shrimp and otocinclus. A crew is not a fix for an algae problem, since they eat what grows and not what caused it. Stock it slowly and only once the tank has something to feed them. Copper and many snail medications kill the whole crew at one dose.
Plants
CO2
CO2 is carbon dioxide, the carbon plants build tissue from and the limit on growth in most planted tanks. A tank without injection has only what comes from fish, bacteria and the surface. That is enough for Anubias, java fern, crypts, vallisneria and mosses under low light. Carpet plants and red stem plants under strong light need pressurized injection through a diffuser or reactor. Run it to a drop checker sitting green at around 30 ppm. It goes with the light, because strong light without the carbon to match grows algae instead of plants. Turn the gas off at night when plants are not using it.
Biology
Colony
A colony is a group living as one unit, and the word carries two meanings in the hobby. A coral colony is a single animal made of thousands of polyps that share tissue and a skeleton. Cutting a piece off it is fragging, and the frag grows into a colony of its own. The other meaning is a self-sustaining group of small animals in a tank. Neocaridina shrimp, Tanganyikan shell-dwellers and many killifish are kept as colonies, with every age class in the tank at once. Start a shrimp colony with ten or more, leave the fry alone, and the numbers climb without any work.
Marine
Copepod
Copepods are tiny crustaceans, a millimeter or two long, that live in the rock, sand and refugium of a marine tank. They come out at night in their thousands, eating detritus and algae. Mandarin dragonets, scooter blennies, pipefish and many wrasses feed on them. Most of those hunt all day and cannot be kept on two frozen feeds. The usual advice for a mandarin is a tank at least six months to a year old and 75 gal (280 L) or more. A refugium breeding pods without a break does the same job. Bottled pods seed a new tank.
Fish health
Copper
Copper is the standard cure for marine ich and velvet, and it is poison to invertebrates. It kills snails, shrimp, crabs, corals and the life in live rock at treatment levels. Treat in a bare quarantine tank, never in a reef. Treatment runs at a measured level for two weeks or more, which means a copper test kit rather than the bottle's instructions. Rock, sand and silicone soak it up and leak it back for years. A tank that has seen copper stays a quarantine tank. Some fish take it badly, so dragonets, seahorses, most sharks and rays and some wrasses want a different treatment.
Biology
Coral
Corals are colonial animals in the same group as anemones and jellyfish. A colony is thousands of polyps sharing tissue, and most build a calcium carbonate skeleton under it. Nearly all the corals sold for reef tanks carry zooxanthellae, the algae that feed them sugars from light. That is why lighting decides more than feeding does. The hobby sorts them by skeleton and polyp size. Soft corals bend in the flow and forgive a new tank. Large-polyp stony corals want moderate light and gentle flow. Small-polyp stony corals want strong light and a KH that never swings. Stony corals pull calcium and carbonate out of the water, so a stocked reef needs dosing.
Marine
Coralline algae
Coralline algae is a red algae that lays down a hard calcium carbonate crust in pink, purple and red. It spreads over live rock, the back glass, the overflow and any pump left alone for long enough. It wants the same calcium and alkalinity that stony corals do, near 420 ppm and 8 to 11 dKH, with magnesium around 1300 ppm. It comes in on live rock as spores and turns up weeks later. Shaded rock and the back glass suit it better than a bright open top. Scrape it off the front glass and the viewing panes only. Urchins and some snails graze it down, so check before adding one.
Biology
Corallite
A corallite is the cup of skeleton a single polyp builds and sits in. A stony coral colony is a sheet of them, joined by shared tissue. Corallite size splits the hobby's two stony groups. Large-polyp stony corals carry corallites you can count by eye, and small-polyp stony corals carry ones a millimeter or two across. The shape also names the species. Acropora carry an axial corallite at the tip of each branch and radial ones along the sides. The shape and spacing of those is what separates one acropora from another. A bare white corallite under lost tissue is where recession has already reached.
Biology
Crustacean
Crustaceans are invertebrates with a hard external shell and jointed legs. Shrimp, crabs, crayfish, copepods, amphipods, daphnia and brine shrimp all belong. The shell does not stretch, so they grow by shedding it and hardening a bigger one underneath. A molted shell on the substrate looks like a dead shrimp and is a good sign. Leave it, since the shrimp eats it back for the minerals. Molting is also when they are at risk. A shrimp needs calcium and a steady GH to harden the new shell. A sudden TDS swing during a water change kills them mid-molt. Hold GH between 6 and 12 dGH for Neocaridina.
Plants
Cultivar
A cultivar is a plant variety selected in cultivation and kept going by propagation rather than collected from the wild. The name is written after the species in single quotes, as in Cryptocoryne wendtii 'Tropica' or Bucephalandra 'Brownie Ghost'. The plants are clones of one selected parent, so a named cultivar looks the same wherever it is bought. A wild collection of the same species varies. Trade names are looser than botany, and several bucephalandra names cover one plant. Some names mark a collection locality rather than a selection. A cultivar keeps its parent species' care needs, so a named crypt is grown exactly like the species.
Water chemistry
Cyanobacteria
Cyanobacteria are bacteria that photosynthesize, so they look and behave like algae without being algae. They spread as a slimy blue-green, red or black sheet over sand, rock and slow leaves, and they peel off in one piece. A patch that is back two days after a siphon is normal, since a scrap left behind regrows fast. It grows where the flow is dead, where food rots in the sand and where nitrate or phosphate sits high. Fix the flow first, siphon the sheets out at every water change and cut the feeding back. A blackout or a course of erythromycin clears it, but it returns unless the cause goes with it.
Feeding
Daphnia
Daphnia are small freshwater crustaceans, about 1 to 3 mm across, that swim in short hops. Fish chase them for a long time, which is why keepers use them to work a bored or overweight fish. The shell is chitin, and it moves food through a constipated fish better than anything else in the freezer. They are sold frozen and live, and a live culture in a bucket of green water feeds itself. Daphnia suit most small fish but are too big for day-old fry, so they follow baby brine shrimp rather than replacing them. A culture crashes in a heatwave, so keep a backup jar somewhere cool.
Fish health
Dechlorinator
Dechlorinator makes tap water safe by neutralizing the chlorine and chloramine in it. Both burn gills at tap concentrations, and both kill the bacteria in a filter, so untreated tap water can crash a cycled tank. Chlorine gasses off if water stands for a day. Chloramine does not, and many utilities use it. A conditioner that handles chloramine also locks up the ammonia it releases, which is why the label mentions ammonia. Dose for the whole tank volume when you refill, or treat the bucket first. Most brands work within a minute. Do not use one to hide an ammonia reading, since binding ammonia is not removing it.
Tank setup
Deep sand bed
A deep sand bed is 4 in (10 cm) or more of fine aragonite sand, usually in a sump or refugium. Oxygen runs out a couple of inches down, and the bacteria living there convert nitrate to nitrogen gas. That is the one process in a marine tank that removes nitrate rather than diluting it. It needs sugar-fine sand and a working population of worms and burrowing snails to keep it turned over. A disturbed old bed can release what it has stored, so it is left alone once it is running. Shallow beds of 1 in (2.5 cm) skip the whole thing.
Water chemistry
Denitrification
Denitrification is bacteria breaking nitrate down into nitrogen gas that leaves the water at the surface. It happens where oxygen has run out but nitrate has not, deep inside live rock and at the bottom of a thick sand bed. Marine tanks lean on it, which is part of why a reef holds nitrate under 10 ppm with modest water changes. Freshwater tanks get much less of it. A sand bed that goes fully anaerobic is a different matter. Black sand that smells of rotten eggs is hydrogen sulfide, not denitrification. Porous ceramic media and a deep sand bed of 4 in (10 cm) or more are the usual ways keepers encourage it.
Behavior
Detritus
Detritus is the soft brown sludge of broken-down plant matter, fish waste and old food, also called mulm. It settles in the substrate, behind rocks and inside the filter. It carries bacteria and feeds shrimp, snails and corydoras, and in a planted tank it releases nutrients slowly into the root zone. Too much is still a problem. A thick layer in fine sand or an untouched canister traps waste, pushes nitrate up and makes a tank harder to hold steady. Run a gravel vacuum over the open parts of the substrate at each water change.
Water chemistry
Diatoms
Diatoms are single-celled algae that coat the glass, sand and leaves of a new tank in a brown film. Most tanks get them between week two and week eight, while the filter is still settling. New sand and tap water bring in the silicate they feed on. They wipe off glass with a paper towel and siphon off sand. Nerite snails and otocinclus eat them. The bloom usually clears on its own once the tank matures, so wait it out rather than dosing anything at it. A brown film in an old tank points at high silicate, weak light or an overdue filter clean.
TankBud rating
Difficulty
On TankBud, difficulty is how demanding a species is to keep, rated in four steps. Beginner means it forgives a new keeper's mistakes and takes a range of water. Easy means it is hardy in a stable tank but wants its parameters near the mark. Medium means it needs a mature tank, a particular diet or specific water. Difficult means it needs conditions most keepers cannot hold, such as a wild diet, a very large tank or precise water. The rating covers keeping a species alive and well, not breeding it, which carries its own rating. The beginner-fish list is bounded by difficulty and temperament together.
Marine
Dinoflagellates
Dinoflagellates are single-celled algae that show up in a reef as brown stringy snot with gas bubbles trapped in it. They spread over sand and rock through the day and pull back at night. Most outbreaks follow nitrate and phosphate being driven to zero, which is the opposite of what an algae problem usually means. Raise nitrate to about 5 ppm and phosphate to about 0.05 ppm and hold them there. Add a UV sterilizer for the kinds that swim in the water column, and siphon the mats out daily. Some species are toxic to snails and fish. Clearing dinos takes weeks rather than days.
Water chemistry
Dissolved oxygen
Dissolved oxygen is the oxygen held in the water, and it is what fish take in through their gills. Warm water holds less of it than cool water, and salt water holds less than fresh. Fresh water at 68°F (20°C) holds about 9 ppm, and at 86°F (30°C) only about 7.5 ppm. Surface movement is what puts it back, so an outflow that breaks the surface does more than a deep bubble stream. Fish hanging at the surface and breathing hard is the sign to look for. Heavy stocking, a heatwave and a power cut are the usual causes. An air pump, a spray bar or a fan across the surface all help.
Behavior
Dither fish
A dither fish is a hardy mid-water or top-water fish kept above shy species. Its calm feeding in the open tells them no predator is about. Apistogramma, discus, wild angelfish and many catfish spend the day hidden without dithers and come out with them. A shoal of six to twelve small tetras, rasboras or danios does the job. Size them so the dithers are too big to swallow and too quick to catch. A target fish is the opposite trick, a fish added to take a breeding male's aggression so he does not turn it on the female.
Anatomy
Dorsal fin
The dorsal fin runs along the top of a fish's back, sometimes split into two, and keeps the fish from rolling as it swims. It carries much of what a keeper reads off a fish. A male sailfin molly's dorsal is twice the height of a female's, and a male Apistogramma cacatuoides carries extended dorsal spines. Dorsal shape also separates a true sailfin molly from a common molly. A clamped dorsal held flat to the body is one of the first signs of stress or illness. The small adipose fin behind it, on tetras and catfish, is a separate fin with no spines.
Water chemistry
Dosing
Dosing is adding something to a tank on a schedule instead of all at once. Planted keepers dose liquid fertilizer two or three times a week. Reefers dose calcium, alkalinity and magnesium daily, and a sick fish gets medication on the days the label names. A schedule is what keeps the level steady. Plants and corals use nutrients every day, and one big weekly dose swings the water instead. Measure the tank volume once, write the dose down and keep to it. Doubling a dose to catch up does more harm than skipping it, and two medications dosed together can be worse than either one alone.
Tank setup
Driftwood
Driftwood is aquarium-safe wood used in a layout. Spider wood, manzanita, mopani, bogwood and cholla are the common ones. It leaches tannins for months, tinting the water and pulling the pH down in soft water. New pieces float, so boil them, soak them for a week or two, or wedge them under stone until they waterlog. Many plecos need it. Bristlenose, panaque and the other wood-eaters rasp it and pass it through the gut, and they go hollow-bellied without a piece in the tank. A white bloom of fungus on fresh wood is harmless, and shrimp, snails and otocinclus clear it in a week.
Fish health
Dropsy
Dropsy is fluid building up inside a fish until the body swells and the scales lift away from it. Looked at from above, the fish looks like a pinecone. It is a sign rather than a disease, and what lies behind it is usually kidney or organ failure. A bacterial infection is often part of it. Goldfish and bettas are the ones keepers see it in most. By the time the scales lift, most fish do not recover. Move the fish to a quarantine tank, keep the water clean and warm, and stop feeding heavily. Epsom salt baths and kanamycin are what keepers try, and neither works often.
Behavior
Dwarf cichlid
Dwarf cichlids are the cichlids that stay under about 4 in (10 cm) and can share a tank with tetras. Apistogramma, the rams and the kribs are the ones most shops carry. They hold a bottom territory around a cave or a leaf pile. A 20 gallon (76 liter) tank suits one pair, and 40 gallons (151 liters) suits a harem. Most want soft, acidic water to spawn, though tank-bred rams and kribs will breed in tap water. They ignore mid-water fish and chase whatever comes near the cave. A cory or a pleco on the same floor is the fish that takes the pushing.
Breeding
Egg layer
An egg layer lays eggs and fertilizes them outside the body rather than giving birth to live young. That covers almost every aquarium fish outside the livebearers. Within the group the habits differ. Egg scatterers leave the eggs where they fall, and cichlids and many catfish guard a clutch on a stone or in a cave. Killifish bury eggs in peat that survives months out of water, and gouramis and bettas hold them in a bubble nest. What they share is a separate egg stage, so a breeder has eggs to protect before there are fry to feed.
Breeding
Egg scatterer
An egg scatterer releases its eggs loose over plants, substrate or open water and gives them no care at all. Most tetras, barbs, danios and rasboras breed this way. The parents eat the eggs within minutes. Breeders spawn a pair or a group over a mesh, a layer of marbles or a clump of java moss. The eggs drop through, and the adults come straight back out. The eggs hatch in 24 to 48 hours in most species. The fry hang on the glass for another two or three days before they swim free and need feeding.
Plants
Emersed
Emersed means grown above the waterline with leaves in the air, the way nurseries raise most aquarium plants. Emersed plants grow faster and ship without algae, which is why farms do it. The emersed leaves are thicker, waxier and a different shape from the submersed ones. Once planted under water the plant drops them over two to six weeks and grows a new set. That change is normal, and it is most of what a new keeper reads as a dying plant. Crypts, swords and most stem plants arrive emersed, while mosses, Vallisneria and many tissue-culture cups do not. Leave the plant in place, trim what melts, and wait for the submersed growth.
Biology
Endemic
A species is endemic to a place when it is found there and nowhere else in the wild. Almost every cichlid in Lake Malawi and Lake Tanganyika is endemic to that lake. Sulawesi's cardinal shrimp are endemic to a handful of lakes on one island. The word carries a care instruction. An endemic evolved in one set of conditions, so it usually wants them copied closely. Rift lake cichlids want hard alkaline water, near pH 8.0 in Malawi and 9.0 in Tanganyika. Sulawesi shrimp want 82°F (28°C) and a pH near 8. Endemics are also the species most exposed to collection pressure, which is a reason to buy captive-bred.
Plants
Epiphyte
An epiphyte grows attached to wood or stone instead of rooted in the substrate, taking its nutrients from the water column. Anubias, java fern, bucephalandra, Bolbitis and the mosses all do it. Tie them with thread or fishing line, or glue them with cyanoacrylate, until the roots grip. That takes a month or two, and then the tie can come off. They are the plants for a bare-bottom or sand tank, for a cichlid tank where everything gets dug up, and for hardscape-heavy layouts. Most are slow and low light, so they collect algae on old leaves under a strong fixture. Give them liquid ferts rather than root tabs.
Tank setup
Established tank
An established tank has been running long enough for the biology to fill in. Cycled bacteria are the first part, and they take four to six weeks. Biofilm on the glass and wood, algae on the rock and a population of microfauna take months more. Several animals will not settle without it. Otocinclus starve in a tank under about six months old, and baby shrimp eat biofilm and nothing else. A mandarin dragonet wants a tank a year old, breeding copepods without a break. Marine keepers use six months to a year as the line before adding a difficult fish.
Water chemistry
Estuary
An estuary is the stretch where a river runs into the sea, and the salinity there moves with the tide and the season. Mangrove swamps and tidal creeks are the same habitat. Fish from it are the brackish ones, and they are built to take a change rather than a fixed number. Green spotted puffers, monos, scats, archerfish and figure eight puffers all come from estuaries. Most are sold as freshwater fish and decline over a year or two in it. Keep them at a specific gravity of 1.005 to 1.015, and raise the green spotted puffer as it matures.
Plants
Fertilizer
Fertilizer is what you add to a planted tank to supply what the fish do not. Fish waste covers nitrogen and some phosphate, so the gaps are usually potassium, iron and the trace elements. A liquid all-in-one dosed two or three times a week covers a low-tech tank. Dry ferts are the same nutrients bought as powders and mixed at home, which costs a fraction of the bottles and suits a big tank. Root tabs handle the root feeders. Dosing more than the plants can use feeds algae rather than growth, so match the dose to the light and CO2 the tank already runs.
Biology
Filter feeder
A filter feeder strains particles out of the water rather than picking food off a surface. Clams, sponges, feather duster worms, many corals and the bamboo and vampire shrimp all do it. They need food in suspension and a current to bring it, which is the part a clean tank fails at. A filter feeder starves slowly in a tank with a strong skimmer and no dosing. Feed phytoplankton, powdered coral food or a fine dry food, and turn the skimmer off for an hour after. Bamboo shrimp want a spot in moderate flow where they can hold their fans open.
Equipment
Filtration
Filtration does three jobs at once. Mechanical filtration traps solids in sponge or floss. Biological filtration holds the bacteria that turn ammonia into nitrate. Chemical filtration pulls dissolved things out with carbon, resin or a phosphate remover. The shapes are the choice. A sponge filter runs on air, is gentle enough for fry and shrimp, and costs almost nothing. A hang-on-back hangs on the rim and suits most community tanks. A canister sits under the tank and holds the most media, for anything over about 40 gallons (151 liters). Undergravel and wet-dry filters are older designs still sold. Rinse media in old tank water rather than under the tap.
Behavior
Fin nipper
A fin nipper takes bites out of other fish's fins instead of leaving them alone. Tiger barbs, serpae tetras, black skirt tetras and some puffers have the reputation. Most nipping comes from a schooling fish kept in too small a group. The pecking order that should run inside the school runs at the rest of the tank instead. Ten tiger barbs nip far less than four do. The targets are slow fish with long fins, so bettas, angelfish, guppies and fancy goldfish are the ones that lose. Torn fins open the way for infection, so move the nipper or grow the group rather than treating the damage.
Fish health
Fin rot
Fin rot is a bacterial infection that eats back the edge of a fin, leaving it ragged with a white or red margin. It is an opportunist and takes hold after something else has gone wrong. Torn fins from nipping or a net, ammonia in the water, or a tank that has gone cold all open the door. Bettas, fancy goldfish and angelfish lose the most fin, because they have the most to lose. Clean water is most of the cure, so change 50 percent daily and test for ammonia. An antibacterial medication is for a case that has reached the body. New fin grows back clear and thickens up over weeks.
Fish health
Flashing
Flashing is a fish turning on its side and scraping against rock, sand, wood or the glass. The flank catches the light as it does, which is where the name comes from. It means the skin or the gills are irritated. Ich, velvet and gill flukes all show as flashing before anything is visible on the fish. Ammonia, nitrite and untreated tap water irritate the same way, so test the water first. A single scrape now and then is normal. Several fish flashing repeatedly through the day is worth acting on, and a flashlight in a dark room is the next step.
Plants
Floating plants
Floating plants live on the surface with their roots hanging in the water and their leaves in the air. Frogbit, water lettuce, salvinia, red root floaters and duckweed are the common ones. They take CO2 straight from the air, so they grow fast in any tank and strip nitrate and phosphate as they go. That shade is what settles bettas, apistos and wild-caught fish, and it slows algae on the glass. The catch is light. A thick mat cuts what reaches the plants below, so thin it every week or two. Duckweed is close to impossible to get rid of once it is in.
Tank setup
Flow
Flow is how much the water moves, and it matters as much as temperature for some fish. Hillstream loaches, danios and many rainbowfish come from moving water and want a current to hold station in. Bettas, gouramis, discus and most blackwater fish come from still water. A strong outflow pins them in a corner and wears them out. Plants want enough to carry nutrients to the leaves and no more. A dead corner grows cyanobacteria, and a jet aimed at the sand digs a hole and blows detritus onto the corals. Aim the outflow at the glass, add a spray bar or fit a baffle rather than turning the filter down.
Marine
FOWLR
FOWLR is fish only with live rock, a marine tank run with rock, sand and fish but no corals or ornamental invertebrates. It is the tank for species rated not reef safe. That covers the large angelfish, triggers, puffers, lionfish and the Thalassoma and Coris wrasses that eat coral, clams, shrimp or snails. Without corals the lighting can be plain and the parameters need less precision. Copper treatments are possible too, because no invertebrates are in the way. The fish load is usually heavier. A FOWLR tank leans on a skimmer, more filtration and bigger water changes than a reef of the same size.
Marine
Frag
A frag is a cutting taken from a coral colony, usually glued to a small ceramic or plastic plug. It is the form almost every coral is sold in. Corals regrow from a cut, so a colony can be divided with bone cutters, a band saw or a snapped branch. Both halves recover in a few weeks. Fragging is what makes an aquacultured trade possible, and a frag grown in a tank settles far better than a wild colony. Cut in clean water and glue the base to the plug with cyanoacrylate. Give it low flow and shaded light for a week while the tissue seals.
Breeding
Fry
Fry are newly hatched or newly born baby fish, from the point they swim free and start to feed until they can take adult food. Egg-layer fry are tiny and live off the yolk sac for a few days. After that they need infusoria, green water or liquid fry food. Livebearer and mouthbrooder fry are far bigger at birth and take crushed flake and baby brine shrimp at once. All of them want small feeds several times a day and clean water, which means daily small water changes in a growout tank. In a community tank most fry are eaten within hours, so move or protect a spawn.
Biology
Genus
A scientific name has two parts, the genus first and the species second, as in Betta splendens. The genus is a group of close relatives, and the plural is genera. Above it sits the family, such as Cichlidae for the cichlids or Loricariidae for the plecos. Fish in one genus usually want the same water and behave alike, which is why the name is worth reading. Common names are the problem the system fixes. Plecos are sold by L-number because their common names repeat across species. Bucephalandra trade names change from shop to shop. Every TankBud profile leads with the scientific name, so you can check what you are actually buying.
Water chemistry
GFO
GFO is granular ferric oxide, an iron-based media that phosphate binds to as water flows past. Reef keepers run it when a skimmer and a refugium cannot hold phosphate low enough for stony corals. Put it in a media reactor with enough flow to tumble it gently, not enough to grind it to dust. Start with half the dose on the label. A fast drop from 0.5 ppm to near zero pales stony corals and can kill tissue at the tips. It stops working once it is loaded, and the sign is phosphate climbing again. Freshwater tanks rarely need it, since plants and water changes handle phosphate.
Water chemistry
GH
GH is general hardness, the calcium and magnesium dissolved in your water. Test kits read it in degrees, written dGH, or in ppm; one degree is about 17.9 ppm. Under 6 dGH counts as soft, 6 to 12 dGH as medium, and over 12 dGH as hard. Most tetras, rasboras and dwarf cichlids color up and spawn best under 8 dGH. Livebearers, goldfish and Rift lake cichlids want 10 dGH and up. Shrimp and snails take the calcium for their shells, so a Neocaridina tank is held at 6 to 12 dGH. GH is a separate reading from KH and the two often differ.
Anatomy
Gill cover
The gill cover, or operculum, is the bony flap over the gill chamber on each side of a fish's head. It opens and closes to pump water over the gills, which is why you count a fish's breathing by watching it. A male betta flares his out along with the red membrane underneath to look bigger. The tissue behind it is thin, so it is one of the first places ammonia burn, ich cysts and flukes show up. Fast, shallow movement in a resting fish means it is short of oxygen or its gills are irritated. Gouramis and bettas also breathe air through the labyrinth organ.
Anatomy
Gills
Gills are the stacked red filaments behind the gill cover that pull oxygen out of water and pass carbon dioxide back. Water holds far less oxygen than air, and warm water holds less than cool water. A fish at 82°F (28°C) has less to work with than one at 74°F (23°C). The tissue is thin and unprotected, so it takes damage first. Ammonia burns it, ich and velvet settle in it, and flukes live on it. Fast breathing, gasping at the surface or gills held open all point there. Test ammonia first, add an airstone, and check the temperature before reaching for medication.
Behavior
Grazer
A grazer feeds by picking at surfaces all day rather than waiting for food to drop in. Tangs, otocinclus, nerite snails, mbuna and most plecos feed this way. Their gut wants a steady trickle of algae and biofilm, so two meals a day leave them hungry in between. A grazer in a clean new tank starves quietly, which is what kills most otocinclus in their first month. Put them in a mature tank, keep driftwood and algae wafers available, and clip a sheet of nori for the marine ones. Leaving the back glass unscraped costs nothing and feeds them between meals.
TankBud rating
Growth rate
On TankBud, growth rate is how quickly a plant grows, rated slow, medium or fast. Slow covers Anubias, bucephalandra and the mosses, which add a leaf every few weeks and gather algae on old leaves. Medium covers crypts, swords and java fern. Fast covers most stem plants, hornwort, vallisneria and floating plants, which can double in two weeks. The rating is a tool for a new tank, since fast plants take up the ammonia and nutrients that would otherwise feed algae. A tank is often started heavily planted with them. Fast plants also mean regular trimming, and they only run at that rate with the light and nutrients to match.
TankBud rating
Growth region
On TankBud, growth region is whether a plant grows under water, above it, or either way, rated submersed, emersed, or submersed or emersed. Most aquarium plants carry the third rating, since crypts, swords, Anubias and bucephalandra grow in both states and are farmed emersed before they are sold. Submersed covers plants that only grow under water, such as vallisneria, the mosses and macroalgae. Emersed covers plants sold for paludariums and ripariums that rot when they are held under. The rating is what to check before a plant goes into a tank with an open top or a low water level.
Water chemistry
Hair algae
Hair algae is filamentous green algae, growing as soft strands on rock, wood, slow-growing plants and the substrate. Reefers shorten green hair algae to GHA. It takes hold where light is strong and a nutrient sits spare. In a planted tank that is usually too long a photoperiod with too little CO2, and in a reef it is phosphate. Pull it out by hand or twist it onto a toothbrush at every water change, because removing it is how the nutrients leave. Then cut the photoperiod to six or seven hours, test phosphate, and feed less. Amano shrimp, tangs and rabbitfish all eat it.
Water chemistry
Hard water
Hard water is high in dissolved calcium and magnesium, over about 12 dGH. It usually carries a high KH and a pH above 7.5 with it. Livebearers, Rift lake cichlids, goldfish, most snails and Neocaridina shrimp do well in it. They use the calcium for shell and skeleton, and their color holds. It is stable water, because the KH stops the pH moving. Softening it means RO water or rain, not chemical pH adjusters, which move the number and let it bounce back. Limestone, crushed coral and aragonite sand raise hardness, which is how a Malawi tank is set up on softer tap water.
Tank setup
Hardscape
Hardscape is the wood and stone in a tank, put in before the plants and the fish. It covers driftwood, branches, seiryu and dragon stone, lava rock, slate caves and cholla. It decides how a tank works, not only how it looks. Broken sightlines let a chased fish get out of view. Caves give cave-spawners and nocturnal catfish somewhere to sit out the day, and every branch is a surface for Anubias, bucephalandra, java fern and moss. Some stone changes the water. Limestone, seiryu and coral rock raise hardness and pH, while lava rock, dragon stone and most slate are inert.
Breeding
Harem
A harem is one male kept with several females. Many cichlids, wrasses and anthias form one in the wild, where a male holds a territory and spawns with each female in turn. The reverse, two males to one female, usually ends with the weaker male dead or the single female harassed to death. Mbuna are kept at one male to three or four females, and Apistogramma at one male to two or three. Fairy and flasher wrasses go as one male with several females in a large tank. Many wrasses and anthias are born female and the dominant fish turns male, so a group sorts itself out.
Equipment
Heater
A heater holds the water at a set temperature, which matters because a fish cannot make its own heat. Most tropical community tanks run at 76 to 78°F (24 to 26°C), discus want 84°F (29°C) and a reef sits near 78°F (26°C). Size it at roughly 3 to 5 watts per gallon, more in a cold room. Buy a separate thermometer and read it every day, since a stuck heater cooks a tank and a dead one lets it fall overnight. Two smaller heaters in a big tank fail more gracefully than one large one. A controller cuts the power if the heater sticks on.
Biology
Herbivore
A herbivore lives on algae and plant matter. Tangs, mbuna, most plecos, otocinclus and many marine blennies feed this way. Their gut is long and built for a steady trickle rather than two big meals. Feeding them meaty food is the common mistake, and in mbuna it brings on the intestinal swelling keepers call Malawi bloat. Clip a sheet of nori for the marine ones every day or two. Run spirulina flake, algae wafers and blanched zucchini or spinach for the freshwater ones. Leave the algae on the back glass, since a herbivore in a spotless tank runs out of food between feedings.
Biology
Hermaphrodite
A hermaphrodite carries working male and female organs at the same time. Bladder, pond and ramshorn snails are the common ones, and many can fertilize their own eggs. That is why a single hitchhiker snail becomes a population in a month. Mystery snails and nerites are not hermaphrodites and need a male and a female. Lysmata shrimp, the skunk cleaners and peppermints, are hermaphrodites once they mature, so any two of them will pair. Fish that switch from one sex to the other during life are sequential hermaphrodites, and that is a different arrangement covered under sex change.
Plants
High-tech
A high-tech planted tank runs pressurized CO2, strong light and a daily or near-daily fertilizer dose. Carpets fill in over weeks rather than months, red plants color up, and demanding species stay compact instead of stretching. The cost is attention. CO2 runs on a timer and gets checked with a drop checker. Ferts have to keep up with the growth, and the tank wants trimming every week or two. Miss the CO2 for a few days and algae takes the opening before the plants recover. It is the setup for a carpet and for red stems, and it is a poor choice for a first tank.
Tank setup
Hitchhiker
A hitchhiker is an animal that arrives on live rock, a coral frag, a plant or in the water in the bag. Bristleworms, copepods and small snails are the common reef ones, and most of them work as cleanup crew. Aiptasia is the one to pull out early, because one anemone becomes fifty and stings the corals it touches. Freshwater tanks get bladder and ramshorn snails on plants, plus the occasional dragonfly nymph or hydra. Dip plants and frags before they go in, and look new rock over before it hits the sand. A peppermint shrimp often eats small aiptasia, and a big one takes an injection of kalkwasser paste.
Fish health
Hole in the head
Hole in the head is pitting and erosion that opens along a fish's head and down the lateral line. Oscars, discus and other large cichlids get the freshwater form, and tangs and marine angelfish get the marine one, called HLLE. The freshwater form often has Hexamita in it and answers to metronidazole. Both forms track back to diet and water quality more than to any one bug. High nitrate, a dull dried-food diet and stale water are the usual background. Feed a varied diet with vegetable matter, keep nitrate low and change more water. Some keepers link heavy activated carbon use to the marine form, so it is worth pulling.
Marine
Host anemone
A host anemone is one of the small number of anemone species that clownfish live in. There are about ten of them, and not every clownfish takes every one. Bubble tip anemones host most of the common clownfish and are the easiest of the group to keep. Carpet anemones host more species, but they grow to a foot across and eat fish. An anemone wants a mature tank, strong light and clean water, so keepers wait six months to a year before adding one. It walks where it likes until it settles, so screen every pump intake first. A tank-bred clownfish may never take one, and it does not need one.
The trade
Hybrid
A hybrid is the offspring of two different species, deliberate or accidental. The flowerhorn, the blood parrot and most mixed Central American cichlids are hybrids. Swordtails and platies cross freely, and many shop angelfish and discus carry mixed ancestry. Some are sterile and some are not. The fertile ones are why an unlabeled fish can carry genes from a species nobody intended. Lake Malawi and Tanganyika species hybridize readily in a mixed tank, which is how many shop mbuna lost their identity. Anyone planning to sell fry keeps one species per group in a tank.
The trade
L-number
An L-number is a catalog number given to a loricariid catfish whose species has not been formally described. The German magazine DATZ started assigning them in the 1980s and the trade uses them still. L046 is the zebra pleco, L200 the green phantom and L134 the leopard frog. LDA numbers come from a second magazine's list. They are photo records rather than taxonomy, so one fish can carry two numbers. A described species keeps its old L-number in shops long after it has a scientific name. Care differs sharply between numbers, from wood-eating panaques to carnivorous zebras, so the number is what to search on.
Anatomy
Labyrinth organ
The labyrinth organ is a folded, blood-rich organ in a chamber above the gills. It lets a fish take oxygen from air gulped at the surface. Bettas, gouramis, paradise fish and the other anabantoids all carry one. It is how they live in warm, low-oxygen water in rice paddies and swamps. In a tank it means they have to reach the surface, so a lid pressed tight to the water drowns them. It also means the air above the water wants to be near tank temperature. Cold room air on a warm fish is a common cause of respiratory trouble in bettas.
Biology
Larvae
A larva is a young animal built differently from the adult it becomes, and the plural is larvae. Fish fry are not larvae in the strict sense, though the first free-swimming days are often called the larval stage. The word decides which invertebrates you can breed at home. Neocaridina shrimp hatch as miniature shrimp and raise themselves in the tank. Amano shrimp and most marine shrimp hatch as swimming larvae that need brackish or salt water and live food for weeks. Marine fish are the same story, which is why almost every clownfish in a shop is captive-bred and almost every tang is not.
Anatomy
Lateral line
The lateral line is a line of fluid-filled pits along each side of a fish, open to the water through small pores. It senses pressure changes and low-frequency movement rather than sound. A school keeps its spacing on it, a nocturnal catfish hunts on it, and a blind cave tetra lives on it alone. You can often see it as a faint line of dots from the gill cover to the tail. Marine tangs and angelfish get head and lateral line erosion, a pitting along it tied to poor diet, stray voltage and carbon use. Feed nori and vitamin-soaked food, and check for stray voltage before anything else.
TankBud rating
Light
On TankBud, light is how much light a plant needs, rated low light, medium light or high light. Low light covers Anubias, java fern, crypts, mosses and bucephalandra, which grow under a plain aquarium fixture and want no CO2. Medium light covers most stem plants, swords and vallisneria. High light covers carpet plants and red stem plants, which need a strong fixture and usually CO2 with it. Strong light without the carbon to match grows algae rather than plants. The rating is about the plant's needs, not the fixture's watts, since the same light is far weaker at the bottom of a tall tank.
Feeding
Live food
Live food is food still moving when it goes in the tank. Blackworms, daphnia, whiteworms, grindal worms, microworms, fruit flies and baby brine shrimp are the usual cultures. Movement is what triggers a feeding response. A wild-caught fish, a new import or a fussy killifish takes live food when it refuses everything else. It is also how fry are raised and how a pair is conditioned before spawning. Culture what you use rather than buying it weekly, since a jar of microworms or a grindal box costs nothing to run. Rinse anything collected from outdoors, and never feed from a pond that holds fish.
Marine
Live rock
Live rock is porous calcium carbonate rock, old reef skeleton, carrying the bacteria, sponges, worms and copepods that make a marine tank work. It is the biological filter and the aquascape at once. The pores hold the bacteria that process ammonia and, deeper in, the ones that reduce nitrate. Most tanks now start with dry rock and seed it from a piece of cured live rock or a bottled culture. That takes longer and avoids aiptasia, bristleworms and hitchhiking crabs. The old rule of thumb is 1 to 1.5 pounds per gallon, and many tanks now run on less. Stack it so water moves through it and no pocket traps detritus.
Marine
Live sand
Live sand is aragonite sand that already carries nitrifying bacteria, and sometimes worms and copepods with them. Bagged live sand from a shop holds bacteria in water and little else alive. Sand taken from a running tank carries the whole community. It shortens a cycle by days rather than weeks, since the rock does most of that work. Dry aragonite sand in a tank with live rock goes live on its own within a month. A bed of 1 to 2 in (2.5 to 5 cm) suits most reef tanks and stays easy to clean. Deeper beds are run for denitrification and need to be left undisturbed.
Breeding
Livebearer
A livebearer gives birth to free-swimming young rather than laying eggs. Guppies, mollies, platies, swordtails and Endlers are the group, along with halfbeaks and goodeids. The male fertilizes the female with a modified anal fin called the gonopodium. She carries the brood about four weeks, then drops twenty to a hundred fry that swim and feed at once. Females store sperm and keep dropping broods for months after the last male has gone, which is why a shop female usually arrives pregnant. Most livebearers want hard water and two or three females per male.
The trade
Locality
A locality is the collection point a wild fish or plant came from, written after the name: Apistogramma agassizii 'Alenquer' or bucephalandra 'Kedagang'. Populations of one species from different rivers often differ in color, size and temperament, and some turn out to be separate species later. Keepers who breed them keep the localities apart, since crossing two loses both and the fry cannot honestly be sold as either. A locality on a label is worth paying for if you plan to breed, and worth nothing if you do not. Plants are sold the same way, with bucephalandra and cryptocoryne named for the stream they came from.
The trade
Long-fin
Long-fin varieties carry fins that grow several times the length of the wild form. They are sold as veiltail, half-moon, long-fin or sailfin depending on the species. Veiltail and half-moon bettas, long-fin bristlenose plecos, long-fin danios, guppies and angelfish are the common ones. The fins slow the fish and tear on sharp decor and strong flow. These varieties want still water, smooth hardscape and no fin-nippers, because tiger barbs and serpae tetras strip a veiltail betta. Torn fins regrow over a few weeks in clean water. A long-finned fish is also poorer at escaping a tank mate.
Plants
Low-tech
A low-tech planted tank runs without injected CO2, on modest light and a light fertilizer schedule. Anubias, java fern, crypts, vallisneria, mosses and most floating plants grow well on what the fish and the air provide. Growth is slow, which is the point. A trim every month or two is the whole job, and no gas bottle runs out on a weekend. The limit is the plant list. Carpeting plants, most red stems and anything sold as demanding will either melt or grow leggy without CO2. A low-tech tank takes months to fill in, and then it stays looking much the same.
Marine
LPS
LPS means large-polyp stony corals, the group with fleshy visible polyps on a hard skeleton. Hammer, torch, frogspawn, candy cane, acans, favia and most brains are the common ones. They sit in the middle of the reef difficulty range, easier than small-polyp stony corals and less forgiving than softies. They want moderate light, gentle flow and KH between 7 and 11 dKH. Many carry long sweeper tentacles that sting at night, so give them several inches of clear water. Most take a meaty feed of mysis. A euphyllia that stays shut is usually stung or sitting in too much flow.
Marine
Macroalgae
Macroalgae are the large marine algae a keeper grows on purpose, rather than the film that needs scraping off. Chaetomorpha is the usual one, a green tangle that grows in a refugium under a light. Caulerpa grows faster and can go sexual overnight, dumping spores and crashing water quality. Halimeda lays down calcium carbonate and uses up calcium as it grows. They take nitrate and phosphate up into their tissue, and harvesting a handful is how those nutrients leave the tank. Run the refugium light on a reverse cycle to steady the pH overnight. Most reef fish leave macroalgae alone, and tangs and rabbitfish eat it.
Biology
Mantle
The mantle is the soft tissue that lines a mollusk's shell and builds it. In snails it sits mostly out of sight. In tridacna clams it is the whole show, a broad colored flap the clam spreads into the light every morning. That tissue is packed with zooxanthellae, so the clam feeds on light the way a coral does. The mantle is also the health check. A maxima clam that stops extending, gapes, or shows a bleached patch is reacting to light, flow or a parameter swing. Give a clam strong light, gentle flow and calcium and KH held where the corals want them.
Behavior
Mbuna
Mbuna are the rock-dwelling cichlids of Lake Malawi, and the name is Tonga for rockfish. Yellow labs, demasoni, red zebras and auratus are the common ones. They rasp algae off the stone all day, and each male holds a patch of it. A tank of them runs on crowding, since a dozen or more in 55 gallons (208 liters) spreads the aggression thin. Malawi's other two groups are kept differently. Haps are open-water fish that want swimming room, and the peacock cichlids of the genus Aulonocara hunt invertebrates over sand and stay calmer. All three are mouthbrooders, and all three want hard, alkaline water.
Plants
Melt
Melt is when a plant drops its old leaves, leaving bare stalks and mush, after a change in conditions. A move from emersed to submersed growth does it, and so does a new tank, a big water change or a shift in light. Cryptocoryne is known for it, which is where crypt melt comes from. Tissue-culture plants often lose their first set of leaves the same way. The roots are usually alive, so leave the plant in place and siphon the rotting leaves out. Hold conditions steady and new submersed leaves appear in two to six weeks. Pulling and replanting restarts the whole cycle.
Feeding
Micro pellets
Micro pellets are pellets under about 1 mm across, made for nano fish and small community fish. Chili rasboras, ember tetras, pygmy corydoras, sparkling gouramis and Neocaridina shrimp all take them. A standard community pellet is too wide for those mouths. A fish that cannot swallow one spits it out and goes hungry beside a full tank. Most brands sink slowly, which suits mid-water fish, and a few float. Feed what the group finishes in about two minutes, once or twice a day. Crushed flake does the same job for less money but fouls the water faster.
The trade
Morph
A morph is a distinct color or pattern form within one species, either found in a wild population or fixed by breeders. The designer clownfish are morphs of the ocellaris clownfish, including snowflake, black ice and wyoming white. Coral names such as rainbow or jack-o-lantern are morphs of one coral species. The animal is the same species with the same care needs, so a morph does not change temperature, diet or reef safety. Price follows rarity rather than difficulty. The names come from the trade rather than from taxonomy, so one fish carries different names between sellers.
Breeding
Mouthbrooder
A mouthbrooder carries its eggs and newly hatched fry in its mouth until they can fend for themselves. It is most often the female, and she eats little or nothing while she holds. Most Lake Malawi and Lake Victoria cichlids brood this way. The female picks up the eggs as she lays them and holds them for three to four weeks. The fry she releases are already 1 cm long and able to eat crushed flake. Some fish use the male instead, including the Betta species, the arowana and some catfish. In a tank a holding female hides and shows a swollen throat. She needs somewhere calm, and breeders often move her to her own tank to spit the fry.
Feeding
Mysis
Mysis are small shrimp about 1 cm long, sold frozen in cubes or flat packs. They carry more protein and fat than brine shrimp and hold their vitamins better, which makes them the staple frozen food in marine tanks. Nearly every clownfish, wrasse, goby and anthias eats them without any coaxing. LPS corals take a piece dropped on the polyp. Thaw a cube in tank water and pour the pack juice off, since it goes straight to nitrate and phosphate. Feed once a day, or twice for anthias and dragonets. Freshwater fish over about 2 in (5 cm) eat them too.
Tank setup
Nano tank
A nano tank is a small tank, usually taken as anything under about 10 gal (38 L). It is stocked with fish, shrimp and corals that stay under 2 in (5 cm). Chili rasboras, ember tetras, pygmy corydoras, sparkling gouramis and Neocaridina shrimp suit one. In saltwater that means clown gobies and a few softies. Less water means faster swings, so temperature, evaporation and a missed water change all hit harder, and a heater failure shows the same day. It suits one species group rather than a mixed community. It still wants a filter, a heater and the same weekly 25 to 50 percent water change.
Water chemistry
New tank syndrome
New tank syndrome is what happens when fish go into a tank before the filter has cycled. Ammonia climbs for the first week or two, then nitrite climbs as the second group of bacteria catches up. Fish gasp at the surface, clamp their fins, go off food and die in ones and twos. The tank often looks fine, with clear water and a filter running. Test ammonia and nitrite rather than trusting the look of it. The fix is a 50 percent water change every day the readings are above zero. Feed lightly and add no more fish until both read zero. Seeded media from a running tank ends it in days.
Water chemistry
Nitrate
Nitrate is the end product of the nitrogen cycle and the reading that climbs between water changes. It is far less toxic than ammonia or nitrite. Most freshwater fish are fine under 40 ppm. Shrimp and sensitive species do better under 20 ppm, and reef tanks run lower again. Nothing in an ordinary filter removes it. A weekly change of 25 to 50 percent is how it comes down, and fast-growing plants take up a share. Tap water in farming country can arrive at 20 to 40 ppm, so test the tap before blaming the tank.
Water chemistry
Nitrite
Nitrite is the second step of the nitrogen cycle and the middle reading on a test kit. Bacteria make it as they break ammonia down. It is toxic above 0 ppm because it binds to the blood and stops it carrying oxygen. Fish gasp at the surface with pale gills. A second group of bacteria turns it into nitrate, and they are slower to establish. That is why a fishless cycle shows nitrite for a week or two after the ammonia has gone. A cycled tank reads 0 ppm, so a reading in an established tank means filter bacteria have been lost.
Water chemistry
Nitrogen cycle
The nitrogen cycle is the bacterial chain that turns fish waste into ammonia, then nitrite, then nitrate. Two groups of bacteria run it, living on the filter media and every surface in the tank. Growing them takes four to six weeks, and that wait is called cycling. Dose ammonia to 2 to 4 ppm and test every few days. The tank is cycled once it clears that dose to 0 ppm ammonia and 0 ppm nitrite within 24 hours. Seeded media from a running tank cuts the wait to days. Rinse filter media in old tank water and never under the tap, because the bacteria live on surfaces rather than in the water.
Behavior
Nocturnal
Nocturnal fish are active at night and hidden by day. Many plecos, most synodontis catfish, kuhli loaches, some eels and many marine crustaceans feed once the lights are off. A keeper can go weeks without seeing a fish that is perfectly healthy. They need somewhere dark for the day: caves, wood, overhangs or dense planting. Their food has to reach them. Drop sinking wafers or frozen food in after lights out, or a fast day fish takes the lot. A dim moonlight brings them out, and so does a few minutes of room light before feeding.
Feeding
Nori
Nori is dried seaweed pressed into sheets, the same product sold for sushi. Buy the plain kind with no oil, salt or seasoning on it. Tangs, rabbitfish, marine angelfish, foxface and many blennies eat it every day in the wild and want it here. Clip a strip to the glass with a veggie clip or a rubber band on a rock. A tang left on frozen food alone loses color and picks at corals instead. Feed a strip every day or two and pull anything left after a few hours. Green and red sheets both work, and freshwater fish take it too.
TankBud rating
Nutrient uptake
On TankBud, nutrient uptake is where a plant takes its nutrients from, rated root feeder, water column, or root + water column. Root feeders are the crypts, swords and most bulb plants. They want a nutrient substrate or a root tab under the crown every few months. Water column feeders are the epiphytes, mosses, floating plants and most stem plants. They take what they need from liquid fertilizer, so they work in a bare-bottom or sand tank. Plants rated for both use either and do best with the two together. The rating decides how a tank is fertilized, because liquid ferts do nothing for a sword in inert gravel.
Breeding
Pair bond
A pair bond is two fish that pick each other and stay paired. Cichlids and clownfish are the usual examples, and a bonded pair defends one territory, spawns on a cycle and raises the fry together. Pairs form on their own. Keepers buy six young angelfish or discus and wait for two to pair off, rather than buying a chosen male and female. A bond can break when the pair is moved, and a male may kill a female he has not bonded with. Once a pair forms it usually lasts for years. A shop selling a proven pair is charging for the wait, not for the fish.
Tank setup
Paludarium
A paludarium is a tank with water at the bottom and land above it, planted both ways. Dart frogs, crabs, mudskippers and small fish live in them, and the land side grows mosses, ferns, Anubias and bromeliads. A riparium is the wetter version, with a normal water level and plants rooted in the water that grow out of the top. Both want high humidity, a glass top and a light that reaches the land plants. The water side is small, so it fouls faster than an aquarium of the same size. A plant rated emersed, or submersed or emersed, is the one that works above the waterline.
Plants
PAR
PAR is short for photosynthetically active radiation, the light in the range plants and corals use. It is measured at a point in the tank with a meter, not at the fixture, so it falls off with depth and with spread. Roughly, 15 to 30 PAR at the substrate is low light, 30 to 50 is medium and above 50 is high. Soft corals sit happily at 50 to 100, and SPS want 200 or more near the top of the rock. Watts and lumens miss this, since lumens are weighted for the human eye and watts say nothing about spectrum. Raising PAR without CO2 and ferts to match grows algae, not plants.
Fish health
Parasite
A parasite lives on or inside a fish and takes what it needs from it. The external ones are ich, velvet, flukes and anchor worm, and the internal ones are camallanus worms, capillaria and hexamita. Flashing against the hardscape, clamped fins and heavy breathing show up before any spot does. Wild-caught fish arrive carrying a load their body has learned to live with, and shipping stress lets it take over. Quarantine every new fish for two to four weeks, and treat marine fish as a matter of course. Copper handles the marine external ones. Internal worms want levamisole or fenbendazole in food.
Tank setup
Peat
Peat is partly rotted sphagnum moss from a bog. Run it through a filter bag and it releases tannins and humic acids. Those pull the pH down, soften the water a little and turn it tea brown. It only works where the KH is low, since carbonates hold the pH up against it. Peat swamps are the flooded forests of Borneo, Sumatra and Malaya, and many wild bettas, rasboras and loaches come from their blackwater. Killifish keepers use peat a second way. Annual killifish lay in a tray of damp peat, which is bagged for weeks or months and then wetted to hatch the eggs. Peat is dug from bogs that do not grow back quickly, so many keepers now use catappa leaves or alder cones instead.
Anatomy
Pectoral fin
The pectoral fins are the paired fins just behind the gills, one on each side. They are used for steering, braking and holding position rather than for speed. Bottom fish rest on them, and plecos, gobies and hillstream loaches prop themselves up on stiffened pectorals. Hillstreams use them as part of a suction hold in current. Male bristlenose plecos and the corydoras carry a thickened pectoral spine they can lock out. That is why a netted cory tangles in the mesh and is better moved in a cup. In corydoras the locked spine is also a defense against being swallowed.
Anatomy
Pelvic fin
The pelvic fins are the paired fins low on the belly, ahead of the anal fin, and older books call them ventrals. A fish uses them with the pectorals to brake, hover and turn. In gobies they are fused into a disc that works as a sucker. That is how a goby holds station on a rock in current. In gouramis they are drawn out into long feelers the fish taps things with, and corydoras and loaches prop themselves up on theirs. Their position varies by family, which is one of the things an identification key uses. They sit under the throat in some fish and well back in others.
Water chemistry
pH
pH tells you how acidic or alkaline the water is. Seven is neutral; lower is acidic and higher is alkaline. Each whole number is ten times the one before it. A fall from 7.0 to 6.0 is a big change for a fish, and a fast one is worse than a low one. Most community fish are happy anywhere from 6.5 to 7.5. Rift lake cichlids want it above 7.8, and wild blackwater fish spawn below 6.0. The number matters less than keeping it still. KH is what holds it there, so a tank with almost no KH can lose a full point overnight.
Water chemistry
Phosphate
Phosphate is a plant and algae nutrient, written PO4 on test kits. It arrives with fish food, with dying plant matter and sometimes with tap water. A planted tank wants some of it. Most liquid fertilizers include it, and a tank sitting at zero stunts stem plants and stalls new growth. A reef tank wants very little. Stony corals slow down and brown out above about 0.1 ppm. Reefers hold it low with a skimmer, a refugium or a phosphate-binding resin. Freshwater keepers rarely test for it, since water changes and plants keep it in check. High phosphate alongside high nitrate is what most algae blooms run on.
Tank setup
Photoperiod
The photoperiod is the number of hours the light runs each day, set on a timer. Six to eight hours suits most planted tanks, and a low-tech tank does well at six. A high-tech tank with CO2 can hold eight or nine. Past that the plants stop gaining and the algae start. A siesta, two shorter blocks with a few hours dark between them, works for the same total. Reef tanks run eight to ten hours of white light with a longer blue period around it. Change the photoperiod by half an hour at a time and wait two weeks before judging it.
TankBud rating
Placement
On TankBud, placement is where a plant goes in the layout, rated foreground, midground, background, floating or epiphyte. Foreground plants stay under about 4 in (10 cm) and carpet or clump at the front. Midground plants fill the middle at 4 to 10 in (10 to 25 cm). Background plants grow tall enough to hide the equipment along the back glass. Floating plants sit at the surface, shading the tank and taking nutrients straight from the water. Epiphyte means the plant attaches to wood or stone rather than rooting anywhere. It can sit at any height in the layout.
Biology
Plankton
Plankton is the drifting life of open water, too weak to swim against a current. Phytoplankton is the single-celled algae half, and zooplankton is the animal half, from copepods to the larvae of crabs and fish. Reef keepers buy both in bottles. Phytoplankton feeds clams, sponges and the copepod population, and zooplankton feeds corals and small fish directly. Most freshwater tanks need none of it, though green water is phytoplankton and it raises fry well. Dose a reef tank after lights out, when the polyps are open and the skimmer is off for an hour.
Marine
Polyp
A polyp is the individual coral animal, a small sac with a ring of stinging tentacles around a single mouth. A colony is thousands of them sharing tissue and a skeleton. Each one catches food and hosts the symbiotic algae that feed it with light. Polyp size is how the hobby splits stony corals. Large-polyp stony corals carry fleshy polyps you can see, and small-polyp stony corals carry tiny ones over a branching skeleton. Polyp extension is the daily health check. A coral with its polyps out is settled, and one closed for days is reacting to flow, light, a parameter swing or a neighbor's sting.
Equipment
Powerhead
A powerhead is a submersible pump that moves water around a tank rather than through a filter. Reef keepers run two or more, aimed to cross in open water so no corner goes still. Detritus then stays in suspension long enough for the filter to catch it. A wavemaker is a powerhead with a controller that pulses or alternates the pumps, which reads more like a reef than a constant jet does. SPS tanks run high turnover, often 20 times the tank volume an hour or more, and soft corals want far less. In freshwater a powerhead is for hillstream loaches, river tanks and mbuna, and it is the wrong thing to point at a betta.
Plants
Propagation
Propagation is making more plants from the ones already in the tank, the ordinary way a planted tank fills in. The method follows the plant. Stem plants are cut and the top half replanted. Rosette plants send runners that are separated once the daughter has roots. Anubias, bucephalandra and java fern are divided by cutting the rhizome into pieces of three or four leaves. Java fern and Bolbitis grow plantlets on old leaves, and bulb plants make offsets. Take cuttings from healthy growth rather than the shaded bare stems, and expect a week or two of nothing while the cutting roots.
Equipment
Protein skimmer
A protein skimmer pulls waste out of the water before the filter turns it into nitrate. A pump chops air into fine bubbles inside a column, and dissolved organics stick to the bubble surfaces. The foam rises into a cup that you pour out, and what collects is dark and smells bad. It works in salt water because seawater makes a stable fine foam, and it barely works in fresh water for the same reason. Size it for the tank and the feeding rather than the tank alone. Give a new one a week or two before judging it. Empty the cup before it overflows into the sump.
TankBud rating
Rarity
On TankBud, rarity is how easily a species is found for sale, rated very common, common, rare or very rare. Very common means any shop stocks it. Common means most shops, or an easy online order. Rare means specialist sellers, a wait, or a seasonal import. Very rare means a species seen a few times a year, usually a wild import or a collector's fish. It describes availability in the hobby rather than conservation status, so a fish can be common in the trade while its wild population is protected. Rarity tracks price more closely than difficulty, and many rare fish are easy to keep once found.
TankBud rating
Reef safe
On TankBud, reef safe is a marine species' rating for life in a tank with corals and ornamental invertebrates. Reef safe means it leaves corals, clams and shrimp alone. Reef safe with caution means it is safe with corals but may eat small shrimp or snails, or nip at some coral types. Not reef safe means it eats coral, clams or invertebrates outright and belongs in a fish-only tank. The rating is set per species from published keeping records, not from size or diet alone, and it appears only on saltwater rows. It is a keeper's convention rather than a scientific category, so a species another site calls reef safe may carry a caution here.
Tank setup
Reef tank
A reef tank holds corals and invertebrates alongside the fish, which sets every other decision. Every fish in it has to be rated reef safe, so angelfish, triggers and most puffers are out. Copper can never go in the display, so quarantine is a separate tank. Corals need a reef light, turbulent flow and KH between 7 and 11 dKH with no swing. Stony corals pull calcium and carbonate out daily, so a stocked reef doses or runs a reactor. Salinity sits at 1.025 specific gravity and temperature near 78°F (26°C). Start with soft corals and LPS rather than acropora.
Marine
Refugium
A refugium is a lit side chamber, usually a section of the sump, where macroalgae grows out of reach of the fish. Copepods and amphipods breed in it. Chaetomorpha under a light on a reverse cycle takes up nitrate and phosphate. Harvesting a handful every week or two is how those nutrients leave the system. The pod population it feeds is what keeps a mandarin dragonet and the other pod-eaters fed. It holds a little rubble rock and no flow strong enough to pin the algae against a baffle. The reverse light cycle steadies pH overnight.
Plants
Rhizome
A rhizome is the thick horizontal stem that Anubias, java fern, bucephalandra and Bolbitis grow from. Leaves rise off the top and roots reach down from the underside. It has to stay above the substrate, because buried under sand or gravel it rots within weeks. That is the most common way a new keeper loses an Anubias. Tie or glue it to wood or stone and let the roots find their own hold. It is also how these plants are propagated. Cut the rhizome with a blade so each piece keeps three or four leaves.
Water chemistry
Rift lakes
The Rift lakes are Malawi, Tanganyika and Victoria, the three big lakes of east Africa. All three hold hard, alkaline water, and their cichlids are kept in it. Malawi runs near pH 8.0 and Tanganyika higher, closer to 9.0. Victoria is the softest of the three. Keepers hold those numbers with crushed coral or aragonite in the substrate, or with a Rift lake salt mix. Plain soft tap water lets the pH drift down and the fish lose color and condition. A Rift tank is usually stocked from one lake, since fish from different lakes want different hardness and different tank mates.
Water chemistry
RO water
RO water is reverse osmosis water, tap water pushed through a membrane that strips out hardness, nitrate, phosphate, chlorine and most metals. What comes through reads near 0 ppm TDS. An RO/DI unit adds a resin stage and gets closer to zero, which is the reef standard. It is not used neat, because fish and shrimp need minerals. Remineralize it with a GH or KH salt to the target the species wants, or cut it with tap water. Keepers turn to it when the tap is too hard for soft-water fish or carries nitrate or phosphate. A Caridina tank needs a precise GH, so it runs on remineralized RO.
Plants
Root tab
Root tabs are fertilizer capsules pushed into the substrate under a plant that feeds through its roots. Swords, crypts, bulb plants and dwarf sagittaria take most of what they need that way, and liquid fertilizer in the water does little for them. Push one into gravel or sand an inch or two from the crown, deep enough that it does not break the surface. One tab covers roughly a 4 in (10 cm) circle and lasts about three months. A tab that leaks into the water column feeds algae, so bury it properly and leave it alone. An aquasoil tank does not need them for the first year.
Plants
Rosette
A rosette plant has leaves rising in a circle from a single crown sitting at substrate level. Crypts, Amazon swords, vallisneria and sagittaria all grow this way. Plant the crown so the roots are covered and the crown itself is not, because a buried crown rots. Most are root feeders and want a nutrient substrate or a root tab under them rather than liquid ferts alone. They take weeks to settle before they push new leaves. They spread by runners rather than cuttings, so propagation means separating a daughter plant once it has roots of its own.
Plants
Runner
A runner is a horizontal shoot a plant sends out along or under the substrate, with a daughter plant growing at the end of it. Vallisneria, sagittaria, crypts, dwarf hairgrass and most carpet plants spread this way. A settled vallisneria throws a runner every week or two and crosses a tank in a season. Leave the runner attached until the daughter has its own roots and two or three leaves. Cut it with scissors rather than pulling, which tears the parent's roots out. In a carpet the runners are left alone, since that is what fills the gaps between the plugs.
Water chemistry
Salinity
Salinity is how much salt is dissolved in the water. A refractometer reads it in parts per thousand, written ppt, and a hydrometer reads the same water as specific gravity. Full-strength seawater is 35 ppt, where reef tanks and most marine fish are kept. Fish-only tanks are sometimes run near 30 ppt to slow parasites. Brackish tanks sit between fresh and marine, roughly 5 to 20 ppt. Corals and invertebrates have no tolerance for swings. Top evaporation up with fresh water rather than salt water, because the salt stays behind when water evaporates and the salinity climbs.
Behavior
Schooling
Schooling fish swim as one group, all facing the same way and turning together. Cardinal tetras and rummynose tetras do it all day. It is how they stay safe from predators, so a schooling fish kept in twos and threes reads the tank as dangerous. It hides, loses color and takes its nerves out on its tank mates. Six is the working minimum, and a dozen settles them faster. TankBud's stocking calculator applies the same rule to schooling and shoaling species. Tiger barbs and serpae tetras mostly nip fins when they are kept below that number.
Breeding
Sequential hermaphrodite
A sequential hermaphrodite is a fish that changes sex during its life, which decides how you stock it. Clownfish are protandrous, meaning they start male. In a pair the larger fish turns female, and that change cannot go back, so two females will fight until one dies. Most wrasses and the anthias are protogynous and start female. The dominant fish of a group turns male, takes on male color and holds a harem. One male with several females works for them, and a second male usually does not. A few gobies and dottybacks can change in both directions. Buy a group of small ones and let them sort it out.
Biology
Sessile
A sessile animal is attached in one spot and cannot walk away from a problem. Most corals, clams, sponges, feather dusters and barnacles live this way. Placement is the whole decision for them. A coral put under too much light bleaches, and one in a dead corner starves. One placed within reach of a neighbor gets stung. Work out the light and flow a coral wants before you glue it down. Anemones are the exception that catches people out, since they walk until they find a spot they like. A wandering anemone finds a powerhead intake, so screen every pump in the tank.
Behavior
Shoaling
Shoaling fish stay loosely together with their own kind without the coordinated turns of a school. They feed and rest near each other, then scatter and regroup as they like. Corydoras, kuhli loaches, yoyo loaches and most barbs shoal. They still need numbers, because a lone one spends the day hidden. Six is the working minimum, and corydoras are kept as six of one species rather than two each of three. TankBud rates shoaling separately from schooling, and the stocking calculator asks for the same six or more.
TankBud rating
Social behavior
On TankBud, social behavior is how a species lives with its own kind: schooling, shoaling, social, or solitary. Schooling fish swim as one coordinated group and fall apart in small numbers, so they are kept in six or more. The catalog's group-size math treats shoaling the same way. Shoaling fish stay loosely together without moving as one. Social species are content in company but do not need a group. Solitary species live alone by choice and may fight their own kind. The rating is about the species' own kind, and temperament covers other fish.
Marine
Soft coral
Soft corals build no stony skeleton, so the colony sways with the flow instead of holding a shape. Leathers, mushrooms, zoanthids, xenia, Kenya tree and green star polyps are the ones shops stock. They forgive a young tank. They take less light than SPS, draw little calcium and alkalinity, and handle a swing in the numbers. That is what makes them the corals to start a reef with. The trade-off is that several of them spread. Green star polyps and xenia will cover rock they were never placed on, so keep them on an island of their own. Zoanthids carry palytoxin, so wear gloves when you cut them.
Water chemistry
Soft water
Soft water is low in dissolved calcium and magnesium, under about 6 dGH, and usually low in KH with it. Most tetras, rasboras, dwarf cichlids, wild Betta species and Caridina shrimp come from water like this. They color up in it, and many will only spawn in it, because their eggs often fail to hatch in hard water. Soft water holds pH less firmly, so a tank under 2 dKH can drift down over a week and wants watching. Rainwater, RO water and tap water over granite are all soft. Peat, leaf litter and driftwood soften it a little further while adding tannins.
Breeding
Spawn
Spawning is releasing and fertilizing eggs, and a spawn is the event itself. Fish do it in the water rather than mating internally, livebearers and a few others aside. Most spawn at dawn, after a cool water change, a warm spell or a few days of live and frozen food. That is how breeders trigger it on purpose. The pattern varies by group. Tetras scatter eggs over plants and eat them minutes later, and cichlids clean a flat stone and guard the clutch. Killifish bury eggs in peat, and gouramis and bettas spawn under a bubble nest. Most freshwater eggs hatch in one to four days.
Tank setup
Species tank
A species tank holds one species, sometimes one pair, and no tank mates at all. Puffers, many wild bettas, shell-dwelling cichlids, seahorses and most large predators do better in one. The reason is usually aggression, a diet nothing else can compete with, or a fish shy enough that livelier tank mates keep it hidden. A species tank also makes breeding far easier, since nothing eats the eggs and nothing competes for the cave. It looks emptier than a community tank, so keepers make up for it with hardscape, plants and a bigger group of the one fish. A dozen of one species reads better than one of each.
Marine
Specific gravity
Specific gravity is the density of salt water measured against fresh water. It is the number most hobby tools read instead of salinity in ppt, and 1.026 is about 35 ppt. Reef tanks are kept at 1.025 to 1.026, fish-only tanks anywhere from 1.020 to 1.026, and brackish tanks between 1.005 and 1.015. The reading moves with temperature, so calibrate a refractometer with a 35 ppt standard at room temperature. A swing-arm hydrometer is the least accurate of the three. Evaporation raises it and only fresh top-up water brings it back, because salt does not leave with the water vapor.
Feeding
Spirulina
Spirulina is a dried cyanobacterium, sold as a powder and built into flakes, wafers and pellets. It is high in protein and carotenoids, so it colors fish up as well as feeding them. Mbuna, tangs, plecos, otocinclus and shrimp all do well on it. For a mbuna it matters more than that, since a meaty diet brings on bloat and a spirulina flake does not. Look for it near the top of the ingredient list rather than as a trace. Most community omnivores take a spirulina flake once or twice a week alongside their staple.
Marine
SPS
SPS means small-polyp stony corals, the branching and plating corals with tiny polyps over a hard skeleton. Acropora, montipora, stylophora, pocillopora and seriatopora are the ones you see. They are the demanding end of the reef hobby. They want strong light, strong turbulent flow, and nitrate and phosphate low but not zero. KH has to hold between 7 and 11 dKH without a swing. More than about 1 dKH in a day burns tips and starts tissue loss. They go in mature tanks, usually a year or older, with dosing or a calcium reactor behind them. Montipora and birdsnest are the usual first ones.
Plants
Stem plant
A stem plant grows as an upright stem with leaves along its length, planted in bunches and trimmed to shape. Rotala, ludwigia, hygrophila, bacopa, limnophila and pearlweed are the common ones. They are the fast growers in a planted tank, which is how a new tank outcompetes algae. They feed mostly from the water column. Propagation is a cut. Take the top half of a stem, strip the lowest leaves and push it into the substrate, where it roots in a week or two. They need regular trimming, or the lower leaves shade out and drop and leave bare stalks under a green canopy.
The trade
Strain
A strain is a line within one species bred for a color, fin shape or pattern and kept going by selecting parents every generation. Half-moon and plakat bettas, full red and cobra guppies, and albino or long-fin bristlenose are all strains. It is not a hybrid, because the fish are one species. Crossing two strains gives fertile young that split the traits over the next few generations. Heavily line-bred strains are often shorter-lived and less hardy than the base form, since the traits come with narrow breeding. A strain only holds if the fish are kept apart, because a mixed guppy tank drifts back toward wild-type colors.
Plants
Submersed
Submersed means growing fully under water, with leaves adapted to it. Those leaves are thinner, softer, often darker and a different shape from the emersed ones the same plant grows in air. A plant taking carbon from the water grows more slowly than it did emersed, so a nursery plant slows down once planted. Most plants sold for aquariums grow either way and take two to six weeks to convert, with the old leaves melting off. A few are only ever submersed, including the mosses, vallisneria and macroalgae. Crypts and bucephalandra flower only when they are grown emersed.
Tank setup
Substrate
Substrate is whatever covers the tank floor, from inert sand or gravel to an aquasoil that feeds plants and lowers pH. Aquasoil holds nutrients and softens the water on its own. Sand at 1 to 2 in (2.5 to 5 cm) suits corydoras, kuhli loaches and any fish that sifts or buries. It also keeps waste on the surface where a siphon can reach it. Gravel hides waste and is fine under fish that do not dig. Root feeders such as swords and crypts want 2 in (5 cm) of soil or a root tab under gravel. Epiphytes and stem plants do not. Crushed coral and aragonite raise hardness deliberately.
Breeding
Substrate spawner
A substrate spawner is a fish that lays its eggs in the open, stuck to a flat surface it cleans first. Angelfish use a leaf or a piece of slate, discus use a cone, and convicts use whatever is flat. Both parents usually stay with the eggs, fanning them and eating the ones that fungus. Give a pair a flat rock, a piece of slate or a length of PVC pipe. They pick one and clean it for a day or two before they spawn. The open eggs are easy to watch and easy to lose, since a first-time pair often eats the batch. Most get it right by the third try.
Equipment
Sump
A sump is a second tank plumbed under the display, usually in the cabinet. Water leaves the display through an overflow, runs through the sump and is pumped back by a return pump. Heater, skimmer, media reactors and the top-off all live down there instead of in the display. It adds water volume, which makes every parameter slower to move. The surface skimming an overflow gives also clears the protein film. Most reef tanks run one and many large freshwater tanks do too. A sump needs a drilled tank or a hang-on overflow box. Leave enough spare room in it to hold the water that drains back during a power cut.
Biology
Sweeper tentacles
Sweeper tentacles are long, stinging tentacles a coral extends to reach a neighbor. Euphyllia corals put them out after lights off, and a hammer or torch can reach 6 in (15 cm) or more. Galaxea, favia and some chalices do the same. The sting kills tissue, and the coral on the losing end recedes from that side without ever touching anything by day. A coral that looks fine at 8 pm and shut at 8 am is being stung at night. Leave at least 6 in (15 cm) of clear water around a euphyllia, and check the tank once after dark.
Anatomy
Swim bladder
The swim bladder is a gas-filled sac in the body cavity that holds a fish at the depth it wants without swimming. Some fish fill it by gulping air at the surface, and others move gas in and out through the blood. A few have lost it. Most loaches, many gobies and the hillstream loaches sit on the bottom because of that. The organ sits against the gut, so a swollen or constipated fish loses trim first. Fancy goldfish are the usual case, since a round body folds the gut against the bladder. Feed daphnia and soaked food, and skip a day before treating anything.
Fish health
Swim bladder disorder
Swim bladder disorder is a fish that cannot hold its depth, floating at the surface, sinking to the bottom or swimming nose down. Fancy goldfish and bettas are the ones it happens to. A gut full of food presses on the bladder, which is why overfeeding and constipation are the common causes. Dry food that swells after it is swallowed makes it worse, so soak pellets before feeding. Fast the fish for two or three days, then feed daphnia for the roughage. Fancy goldfish are bred short and round, and the crowded body cavity makes some of them float for life. A fish that tilts after an injury usually stays that way.
TankBud rating
Swim level
On TankBud, swim level is where a species spends most of its time, rated bottom, middle or top. Bottom covers the corydoras, loaches and plecos that work the substrate and the wood. Middle covers most tetras, barbs, rasboras and dwarf cichlids in open water. Top covers hatchetfish, danios, halfbeaks and killifish that hold just under the surface. It is a stocking tool, because a community feeds and looks better when the levels are shared out. The rating also flags conflicts a size comparison misses. Two bottom species in a small tank compete for the same floor and the same sinking food.
Behavior
Symbiosis
Symbiosis is a close, repeated relationship between two species. In mutualism both sides gain, the way a clownfish takes shelter in an anemone and feeds it scraps in return. In commensalism one side gains and the other carries on regardless, which is how a remora rides a shark. Corals and their zooxanthellae are the reef's version. The pistol shrimp that digs a burrow for a watchman goby is the pairing most reef keepers want to watch. Most of the pairs kept in the hobby are marine. TankBud lists the ones it tracks on the symbiotic relationships page, so you can check a pair before buying both halves.
TankBud rating
Tankmates
On TankBud, tankmates is how a species fits with other species in a shared tank, rated community safe, with caution, or species tank only. Community safe means it can be stocked with other peaceful fish of a similar size. With caution means it needs a chosen list, because too big, too small, too slow or too long-finned brings trouble. Species tank only means it takes a tank alone or with its own kind. That covers fish that swallow anything they can fit in, and fish that attack everything. Temperament describes the behavior, and this rating is the stocking answer that follows from it.
Water chemistry
Tannins
Tannins are the brown compounds that leach out of driftwood, leaf litter and seed pods, staining the water tea-colored. They pull the pH down a little in soft water with a low KH. In hard water they do almost nothing, because the KH buffers against them. They are mildly antibacterial and antifungal. That is why shrimp keepers and betta breeders keep catappa leaves in the tank, and why fewer eggs fungus in tannin-stained water. The color is cosmetic, so carbon or repeated water changes clear it, at the cost of the tannins as well.
Feeding
Target feeding
Target feeding puts food on one animal rather than into the water. Use a turkey baster, a long pipette or a feeding tube, and turn the pumps off for a few minutes first. LPS corals, anemones, sun corals, feather dusters and seahorses are the usual targets. A piece of mysis laid on an open polyp is taken in within a minute. Sun corals need every polyp fed two or three times a week, since they carry no zooxanthellae and live on food alone. Target feeding also keeps waste down, because nothing goes in that an animal is not already holding.
Water chemistry
TDS
TDS is total dissolved solids, everything dissolved in the water added together. That covers hardness minerals, salts, nitrate and fertilizer, all in one number. A pen meter reads it in ppm in a second, which is why shrimp keepers watch it. It does not say what is dissolved, so 250 ppm is hardness in one tank and nitrate in another. Use GH and KH to name the part that matters. TDS is for tracking change. RO water reads near 0 ppm and a settled Neocaridina tank sits at 150 to 250 ppm. A climb between water changes is waste and topped-up minerals building up.
TankBud rating
Temperament
On TankBud, temperament is one of three ratings for how a species treats other fish: peaceful, mostly peaceful, or aggressive. Peaceful species ignore tank mates that are not food-sized. Mostly peaceful species are fine in a community but chase, nip or hold a territory in some situations. That most often happens when breeding, when crowded, or with fish that look like them. Aggressive species attack tank mates as a matter of course and get no tank mate suggestions on their pages. The rating describes behavior toward other species. How a fish treats its own kind is the separate Own kind rating.
Behavior
Territorial
A territorial fish defends a patch of the tank against anything that comes near. The patch is usually a cave, a rock, a piece of wood or a flat stone it has claimed to spawn on. Most cichlids, many plecos and marine damsels hold territory, and it tightens at spawning time. A pair of kribensis that shared a community tank can claim half of a 20 gal (75 L) tank once the eggs are down. Room and sightlines are the fix. Break the floor plan with wood and rock until a chased fish can leave the line of sight. Give every cave-holder a cave of its own.
Plants
Tissue culture
Tissue culture plants are grown in a sealed cup on nutrient gel in a sterile lab, sold as in vitro cups. Nothing lives in the cup, so they arrive with no snails, no algae and no pesticide residue. That matters in a shrimp tank, where a dip for snails would kill the shrimp. The plants are small and were grown in high humidity on sugar rather than under water, so they often melt back before they adapt. Rinse the gel off the roots completely, since it feeds bacteria and algae. Then split the cup into several small portions and plant them spaced out to fill in.
Water chemistry
Trace elements
Trace elements are the minerals a tank uses in tiny amounts, measured in parts per billion rather than ppm. Iodine goes into the tissue of soft corals and into the shell of a molting shrimp. Strontium goes into stony coral skeletons alongside calcium. Iron, manganese and boron matter to plants and macroalgae. A regular water change with a good salt mix puts most of them back, which is enough for most reef tanks. Dosing them blind is where trouble starts, since iodine at too high a level is poisonous and no cheap test kit reads it well. Dose a trace element only when a test or a visible deficiency calls for it.
Tank setup
Turnover
Turnover is the tank volume divided into what the pumps move in an hour. A filter rated at 200 gallons per hour on a 40 gallon tank gives five times turnover. Most community tanks run at four to six times, planted tanks at around ten, and reef tanks far higher. Soft corals sit near ten to twenty times, and an SPS tank runs twenty to fifty with the powerheads doing most of it. Rated flow is measured with no media and no head height, so a loaded canister delivers well under its number. What matters is that no corner sits still.
Water chemistry
Two part
Two part is a pair of reef supplements dosed together, one carrying calcium and the other carbonate. They go in at equal volumes, because the pair is built to keep the ionic balance right. Split the daily amount into several small doses, and add them at different points in the sump. Dosed together in one spot they react and fall out as a white cloud. Test calcium and alkalinity for a week, work out how much the tank uses a day, then set the pumps to match. Two part adds sodium and chloride as it goes, which builds up in a heavily dosed tank and comes back down with water changes.