How to set up a fish tank, step by step

A freshwater fish tank goes together in a set order, and the fish come last. The leak test and the setup itself fill a weekend. After that the tank runs empty while it cycles, with the first fish arriving later in small groups.

1. Choose the tank size and a level spot near an outlet.
2. Fill the empty tank with tap water and leave it for a day to check for leaks.
3. Rinse the gravel or sand and spread it over the bottom.
4. Set the rock and wood in place while the tank is dry.
5. Fill the tank slowly and treat the water with a dechlorinator.
6. Start the filter, then the heater and the light.
7. Put the plants in once the water clears.
8. Let the tank cycle until ammonia and nitrite both read 0.
9. Add the first fish a few at a time.

How big a tank to start with

Extra water dilutes the waste fish make, so a bigger tank rides out beginner mistakes better. One heavy feeding or a skipped water change moves the readings less in 29 gallons than in 10.

Size also decides what can live in the tank. A 10 gallon (38 liter) tank suits nano fish and shrimp, while a 20 or 29 gallon starts to fit a mixed community. Each tank-size page lists the fish that fit, with three plans the stocking calculator checked. Measure the spot before you choose, leaving room above the tank to lift the lid and work inside.

Find a level spot near an outlet

Keep the tank out of direct sun, which warms the water and feeds algae. Heating and cooling vents swing the temperature, and so does an outside door in a cold climate. A tank beside a busy walkway gets bumped. Choose a wall with an outlet in reach, ideally not far from a sink for water changes.

Water weighs 8.34 pounds per US gallon. A 20 gallon tank holds about 167 pounds (76 kg) of water, and a 55 gallon holds about 459 pounds (208 kg). The glass, gravel and rock come on top of that, so a set-up tank runs about 10 pounds per gallon.

Put that weight on a stand built for your tank's size. Check what its maker rates it to carry before the tank goes on. Shim the stand until it sits level and does not rock. Do it while the tank is empty, since a tank out of level puts uneven pressure on its seams.

A framed glass tank must rest firmly on all four corners, while acrylic and rimless tanks can sit on a buffer mat. Ask a structural engineer or a licensed contractor before a large tank goes on an upper floor or into a mobile home.

Check the empty tank for leaks

New tanks leak too, so test yours before anything goes in it. Fill the empty tank to the top with tap water and leave it for 24 hours. Do it somewhere a drip costs nothing, such as a garage floor. Check the seams and the floor under them before you empty it.

A tank that leaks goes back to the store rather than getting patched. Once it passes, empty it and wipe out the dust with plain water. Soap and household cleaners never touch the tank or anything that goes in it.

Gear to have before setup day

Start the list with the filter, which moves the water and houses the bacteria that break down fish waste. A sponge filter, driven by an air pump, is the simplest choice for a first tank. A hang-on-back filter runs on its own motor instead.

A heater holds the temperature your fish list on their profiles. Size it at about 5 watts per gallon in a mild room, and more in a cold one. Add a thermometer at the far end of the tank to check that the heater keeps up.

A light on a plug-in timer gives the tank a regular day and helps control algae. A lid cuts evaporation and heat loss and keeps jumpy fish inside. Pick a test kit that reads ammonia, nitrite, nitrate and pH.

A dechlorinator, often sold as water conditioner, neutralizes the chlorine and chloramine in tap water. To see what the whole list costs, enter it in the aquarium planner, which totals each line as you price it.

Rinse the substrate and spread it out

Bagged gravel and sand carry dust that clouds the water. Rinse them in a colander or bucket under the tap until the water runs clear. Use plain water only, with no soap or bleach. Plain gravel or coarse sand is easier to live with in a first tank than a nutrient-rich soil.

Spread the substrate 2 to 3 inches (5 to 7.5 cm) deep where plants will root. Plain gravel holds no food for plants, so rooted plants such as crypts and swords need root tabs pushed in beside them.

Rock and wood go in dry

Scrub each rock with hot water. Test any rock you are unsure of with a few drops of vinegar. Fizzing means calcium carbonate, which pushes hardness and pH up as it dissolves. Keep fizzing rock and veined rock out of a soft-water tank, since veins can mark metal ores.

Driftwood floats at first. Bogwood and mopani also leach tannins that tint the water brown. Soak the wood in a bucket until it sinks and stops coloring the water.

Set the pieces while the tank is dry and you can still reach the bottom. Leave room by the filter outlet for the heater, and keep rock and wood from touching it.

Filling and treating the water

Pour the water onto a clean plate or plastic bag set on the substrate, so the stream does not dig up the gravel. Fill the tank halfway, fix any decor that shifted, then fill to about 1 inch (2.5 cm) below the rim. Use water near the temperature you plan to keep.

Tap water from a city system carries chlorine or chloramine, both toxic to fish at drinking-water levels. More than one in five Americans drink water treated with chloramine.

Dose the dechlorinator for the whole tank as you fill it. Check that the label names chloramine, since a product that removes chlorine may not treat it.

Start the filter, then the heater

Prime a hang-on-back filter by filling its box with tank water, unless the maker says it primes itself. Plug it in with its drip loop and watch for a steady return flow.

Place the heater near the filter outlet, where moving water spreads the heat. Set the dial, then wait 30 minutes before you plug it in so the glass can match the water temperature. The tank can take up to 12 hours to reach the set temperature, so read the thermometer the next day before you touch the dial.

Set the light's timer to about six hours a day at first. A short day leaves algae in a new tank less light to grow on. Let everything run for a day while you watch for drips around the filter and the seams.

Easy plants for a new tank

Live plants can go in once the water clears, well before any fish. Java fern and Anubias barteri, both rated beginner, grow tied or glued onto rock or wood. Their rhizome rots if it is buried, so keep it above the substrate. Hornwort floats or wedges behind decor and feeds from the water, soaking up ammonia and nitrate as it grows.

Cryptocoryne wendtii goes into the substrate, with the crown above the gravel and a root tab nearby. Most new crypts melt within days of planting. Leave the plant in, since new leaves grow from the roots within two to four weeks.

All four list low light and no added CO2. The beginner plants list has more that forgive a first tank.

The wait while it cycles

The tank is ready for fish once cycling has grown enough bacteria to hold ammonia and nitrite at 0. A fishless cycle takes about four to six weeks, and the cycling guide walks through it step by step.

Choosing the first fish

Pick the whole stocking list now, even though the fish arrive in stages. The stocking calculator rates how full the list leaves the tank and shows where the fish's temperature and pH ranges overlap. It rates every fish at its adult size, so a plan that fits today still fits once they grow.

A checked plan from the 20 gallon page uses only species rated beginner or easy. Seven cherry barbs school in the middle, six panda cories work the bottom and one zebra nerite grazes algae off the glass.

Cherry barbs over panda cories

• 7Cherry barb
• 6Panda cory
• 1Zebra nerite

Comfortable

LightComfortableFullHeavyOverstocked

These species overlap at 72–77°F (22–25°C), pH 6.5–7.5.

Open this plan in the stocking calculator

The beginner list has more fish that suit a first tank. Run any swap through the calculator before you buy.

Beginner freshwater fish →250 species

A few fish at a time

A new filter cannot process much waste at first, so a big batch of fish can push ammonia and nitrite up. Add a few fish at a time, with at least a week between groups. Test ammonia and nitrite before each trip to the store, and hold off while either reads above 0.

The plan above fits three weekly trips. The barbs go in first as one school, since they want a group of six or more. The cories follow a week later. The nerite comes last, once some algae has grown for it to eat.

Acclimating each group

The cup method takes about half an hour. Cut the bag open and pour the fish with some of their water into a clean container.

Add tank water until the level doubles, double it again after 15 minutes and once more after 10. Net the fish into the tank and pour the container water down the sink. Dim the room if they dash around.

Shipped fish go in faster. Float the sealed bag for 10 to 15 minutes to match temperatures, then net the fish across. Opening a shipping bag releases carbon dioxide, so the pH climbs and the ammonia built up during the trip turns more toxic.

The first month

Feed once a day, only as much as the fish finish in about two minutes. Food still on the bottom after five minutes means too much.

Test the water weekly and before each new group of fish. Change 25 to 50 percent of the water each week, which suits most stocked freshwater tanks. The aquarium maintenance log has a sheet for each test and water change, with the schedule TankBud's reminders start from.

Unplug the heater and filter before your hands go in. Refill with dechlorinated water matched to the tank's temperature. Plug the heater back in once the water covers its minimum line.

About once a month, rinse the filter media in a bucket of old tank water rather than under the tap. Tap water can kill the bacteria the filter relies on.

A brown dust on the glass and on older leaves in the first weeks is usually diatoms. They show up in most new tanks and fade on their own as the tank matures.