Clownfish tank setup: tank size, salt water and anemones

An ocellaris or percula clownfish pair needs a saltwater tank of at least 20 gallons (75 liters), and both species grow to about 3.1 inches (8 cm). You don't need an anemone, because most clownfish in stores come from hatcheries, and those captive-bred fish live well without one.

If you'd like the pairing anyway, the usual host is a bubble tip anemone. It needs 30 gallons (115 liters), strong reef lighting and a tank that's run for at least six months. With or without the anemone, the tank itself is a small reef, built on RO/DI water, salt mixed to a measured strength and a finished cycle.

Tank size for a pair

Published minimums for a clownfish pair start at 15 gallons. One UK guide goes higher and wants 21 to 26 gallons (80 to 100 liters) in any first marine tank, so there's room for enough live rock. The ocellaris and percula profiles both list 20 gallons (75 liters).

In a pair, the female grows larger than the male, and together they claim a patch of rock or coral and guard it. Since the temperature and salinity change faster in a small marine tank, it needs closer watching than a larger one.

Clark's and tomato clownfish grow to 5.5 inches (14 cm) and list 30 gallons (115 liters). The maroon clownfish reaches 6.7 inches (17 cm), lists 40 gallons (150 liters) and is marked aggressive, so none of the three fits a 20 gallon tank.

In a 20 gallon tank, the simplest plan is the pair with one skunk cleaner shrimp.

An ocellaris pair with a cleaner shrimp

• 2Ocellaris clownfish
• 1Skunk cleaner shrimp

Comfortable

LightComfortableFullHeavyOverstocked

These species overlap at 75–81°F (24–27°C), pH 8.1–8.4.

Open this plan in the stocking calculator

If you want a little more, one plan on the 20 gallon saltwater page adds a firefish and five snails to this one. Each saltwater tank-size page lists the reef fish that fit, with plans the stocking calculator has checked.

Ocellaris or percula

Most designer clownfish are color lines of these two species. The snowflake, black ice and storm lines come from the ocellaris, while the picasso and platinum lines come from the percula. Each line takes the same care as its parent, so the setup doesn't change.

The two species look nearly alike, but the ocellaris usually has 11 spines in its dorsal fin and the percula typically has 10. The percula's white bars also carry broad black edges, which the ocellaris usually lacks. Their profiles match on adult size, minimum tank, temperature and pH, so pick the one you like the look of.

Keep the two species apart, though, because an ocellaris and a percula wear the same three white bars. In a 2022 experiment, an ocellaris colony attacked a model fish with white bars for longer than one with white stripes.

A wild group is a breeding pair and a few smaller fish that don't breed. The female is the largest, the male comes second, and each fish below them stays smaller than the one above it. In an aquarium, groups of three or more need a large tank and close watching for aggression, so a first tank should hold one pair.

Mixing the salt water

Every batch of salt water should start from RO/DI water, which is tap water filtered down to zero TDS. That's because tap water can carry chlorine, ammonia, nitrate, phosphate, silica and metals such as copper and iron. Several of those feed nuisance algae, and a reef's water can't be cleaner than the water it was mixed from.

Mix the salt in a clean bucket, or in a new tank before any animals go in. For small batches, Instant Ocean's directions give half a cup of salt per gallon. Stir or run a small pump until the salt dissolves, then aerate the water before you measure it.

Read the specific gravity with a refractometer, which has no floating parts and corrects for temperature on its own. Calibrate it about once a month with saltwater calibration fluid rather than RO/DI water. Natural seawater is about 35 ppt, or a specific gravity near 1.026. If the reading comes in low, add salt, and if it's high, add RO/DI water.

pH

7.9 to 8.5

Ammonia

up to 0.02 ppm

Nitrite

up to 0.02 ppm

Nitrate

up to 10 ppm

Temperature

76 to 82°F (24.4 to 27.8°C)

KH

7 to 12 dKH

Phosphate

up to 0.05 ppm

Salinity

1.023 to 1.027

Calcium

380 to 470 ppm

Magnesium

1,250 to 1,400 ppm

Saltwater tanks keeping corals and other sensitive inverts. TankBud reads every water test against these targets when a tank uses this profile.

Evaporation takes only fresh water and leaves the salt behind, so the specific gravity climbs until you top off. A 40 gallon tank can lose about half a gallon a day that way. To keep the reading steady, top off with fresh RO/DI water, or let an auto top-off do it from a reservoir.

A heater holds the water inside the clownfish range of 75–82°F (24–28°C). If a bubble tip and a cleaner shrimp live in the tank too, keep the water within 75–81°F (24–27°C), the range all three share.

Cycling at full salinity

A saltwater tank cycles by the same fishless method as a freshwater one, which the cycling guide sets out step by step. You feed the filter bottled ammonia until it clears a full dose to nitrate within a day. Without bottled bacteria, that takes 30 to 45 days, and salt water usually takes longer.

Make sure to mix the salt to the specific gravity you plan to keep before the first dose, because raising it later can set the filter back. When a 2019 study raised the salinity on working filters, they lost much of their ammonia capacity and regained it only with time.

If you add bottled bacteria, use a culture sold for salt water, since a 1996 study found different ammonia-oxidizing bacteria in marine filters than in freshwater ones.

Live rock brings bacteria and decaying matter in with it, so a tank built on it usually cycles in four to six weeks. Dry rock doesn't bring either, which means it needs bottled bacteria and an ammonia source, and the cycle takes longer. For a first marine tank, you'll want a protein skimmer and as much live rock as you can afford.

Buying and adding the pair

Buy captive-bred clownfish, since they're hardier and more used to tank life than wild ones. Brooklynella, the parasite behind clownfish disease, commonly hits wild-caught clownfish, and once the late signs show, it can kill within hours. Hold any new fish in a quarantine tank first, because it's far easier to treat the disease there than in the display.

Start with two small juveniles of one species and add them on the same day. That works because clownfish are sequential hermaphrodites that mature as males, and the larger fish of the pair turns female. In a 2019 study, juvenile percula paired with a same-size rival grew faster than juveniles kept alone on the same food.

Feed small portions two or three times a day, and only what the pair finishes in a few minutes. They'll take most meaty foods and frozen preparations. When a pair settles in, it may spawn, and both parents then guard the eggs from their tank mates.

A cleaner shrimp and other tank mates

A skunk cleaner shrimp fits in the same 20 gallons (75 liters) and grows to 2.4 inches (6 cm). It'll set up a cleaning station on the rock and pick parasites and dead tissue off the fish, sometimes from inside their mouths.

Bring the shrimp in by drip, because it doesn't handle sudden changes in water quality. The shrimp tank guide walks through the drip method for freshwater shrimp.

Copper medicines kill most invertebrates, so they can't go into a tank with the shrimp or an anemone. Leave hawkfish and lionfish out of this tank, too, since they may eat a cleaner shrimp.

Add any other fish one at a time, about a week apart. If you're stocking more than the pair, a plan from the 30 gallon saltwater page puts a royal gramma and a firefish with them.

Clownfish with a royal gramma

• 2Ocellaris clownfish
• 1Royal gramma
• 1Firefish
• 1Skunk cleaner shrimp
• 3Trochus snail

Comfortable

LightComfortableFullHeavyOverstocked

These species overlap at 75–79°F (24–26°C), pH 8.1–8.4.

Open this plan in the stocking calculator

This mix needs the bigger tank because the royal gramma lists 29 gallons (110 liters). You'll find more fish suited to a first reef on the beginner saltwater list.

Beginner saltwater fish →100 species

Host anemones in the wild and in tanks

Ten anemone species host clownfish on reefs across the Indo-Pacific, but the ocellaris and percula each use only a few of them. The ocellaris lives in the magnificent anemone and two carpet anemones, the gigantea and Mertens', while the percula uses the magnificent, the gigantea and the sebae anemone. The symbiotic relationships page lists the hosts of every clownfish in the catalog.

All four are marked difficult and list 40 to 53 gallons (150 to 200 liters), and both carpets are marked aggressive as well. Mertens' carpet reaches 35.4 inches (90 cm) across. That's three times the width of a bubble tip.

So the bubble tip anemone is the usual tank host instead. Neither fish uses it in the wild, but both take to it in captivity, as most clownfish do.

The hosting instinct is inborn, so captive-bred clownfish keep it without ever learning it from their parents. Some move into a bubble tip, while others settle on a large-polyp stony coral, a xenia or a patch of rock.

Since the bubble tip reproduces by splitting in two, you can buy an anemone that was split in a tank. That's the kind to get, because collecting for the aquarium trade has thinned host anemones on some reefs.

Light, rock and flow for a bubble tip

Give the tank six months to a year of stable water first. The bubble tip feeds partly through the zooxanthellae in its tissue, so it needs strong reef lighting, and about 150 to 200 PAR at the anemone suits it. Under weak light, it stretches its body out to catch more.

A bubble tip anchors its foot deep in a crevice of hard rock and never in sand. So when you build the rockwork, leave holes it can wedge into, in a spot with moderate flow.

A new anemone often walks around the tank before it settles. Once it's settled, though, a fresh move means something is off, so test the water and check the light.

Feed the bubble tip small pieces of meaty food, such as mysis, chopped shrimp or krill, one to three times a week. Offer each piece with tongs and keep it smaller than the anemone's mouth, since an oversized piece can come back up.

The anemone stings any coral it touches, so leave it room on every side. In a small tank, a quiet fish or a shrimp can also drift into its tentacles overnight.