Getting started

How to set up a fish tank: a 10-step checklist for beginners

By The FishFits team · Updated

To set up a fish tank, plan your fish first, then put the tank on a level stand rated for its full weight, roughly 10–12 lb per gallon (1.2–1.4 kg per litre). Add rinsed substrate, a filter rated at about 4–6 times the tank volume per hour, a heater of roughly 2.5–5 watts per gallon (more for a cool room), and tap water treated with dechlorinator. Cycle the tank for about 4–8 weeks until ammonia and nitrite read 0 ppm, then add fish a few at a time, about two weeks apart.

The hands-on part of setting up a fish tank takes one afternoon. Then comes about 4–8 weeks of waiting while the tank grows the bacteria that break down fish waste. Skipping that wait, called cycling, is one of the most common reasons new fish die in their first weeks.

The 10-step checklist at a glance

  1. Plan your fish, then choose the tank size.
  2. Pick a spot that can carry the full weight.
  3. Set up the stand and level the tank.
  4. Rinse and add the substrate.
  5. Fit the filter and heater, but leave the heater unplugged.
  6. Add rock, wood and plants.
  7. Fill with treated water and turn everything on.
  8. Run the tank for 24 hours, then check for leaks and the temperature.
  9. Cycle the tank for about 4–8 weeks.
  10. Add fish a few at a time, about two weeks apart.

What you need before you start

  • A tank with a lid (many fish jump) and a stand rated for its full weight
  • A filter and heater sized for the tank (see the table below), plus a thermometer
  • Gravel, sand or planted-tank soil
  • A light on a timer
  • Water conditioner that treats chlorine and chloramine
  • A liquid test kit for ammonia, nitrite, nitrate and pH
  • A bucket used only for the tank, a gravel vacuum and a net
  • An ammonia source for cycling, or seeded filter media from a healthy tank
  • A spirit level, towels and an outlet with GFCI (ground fault) protection

Step 1: Plan your fish, then choose the tank

Choose your fish before you buy anything, because they decide the tank size, heater, filter flow and substrate. Bottom sifters such as corydoras need sand or smooth gravel. Some shop fish outgrow any starter tank: bala sharks reach about 12 in (30 cm), and a school of five needs around 200 gallons (757 L).

Put your ideas into the stocking calculator. It checks waste load, swimming room, school sizes, compatibility, and the temperature, pH and hardness ranges your fish share. Beginners should aim to stay under about 85% on its meters. Temperature is a common trap: white cloud mountain minnows like 61–72 °F (16–22 °C) and neon tetras like 70–77 °F (21–25 °C), so they only overlap at 70–72 °F (21–22 °C). Also test your tap water’s pH and hardness and pick fish that suit it.

A 20 gallon long or 29 gallon makes a forgiving first community tank. A 10 gallon suits a small group of nano fish, and a 5 gallon suits one betta or a shrimp colony. Compare sizes on our tank size pages.

Step 2: Pick a spot that can take the weight

Water weighs 8.34 lb per US gallon (1 kg per litre). Add glass, gravel and rock, and plan on roughly 10–12 lb per gallon (1.2–1.4 kg per litre). A 55 gallon tank comes to roughly 550–625 lb (250–285 kg) once set up, before the stand, all resting on about 4.3 sq ft (0.4 m²) of floor. The tank weight calculator gives the figure for your exact setup.

  • Floor: put heavy tanks against a wall, ideally a load-bearing one, with the long side across the floor joists so more joists share the weight. For setups over about 1,000 lb (450 kg), upstairs rooms, older homes or floors that bounce, ask a builder or structural engineer before filling.
  • Sunlight: direct sun feeds algae and can overheat a small tank.
  • Drafts and heat: stay away from radiators, heating and AC vents, and outside doors.
  • Access: you want an outlet nearby, a short walk to a tap, and 4–6 in (10–15 cm) behind the tank for a hang-on-back filter and cables.
  • Traffic: a quiet spot keeps shy fish calmer.

Step 3: Set up the stand and level the tank

  1. Put the stand in its final place. Never move a tank with water or gravel in it, because seams can fail.
  2. Check level side to side and front to back. Shim under the stand, never under the tank.
  3. Wipe the tank with plain water only. No soap or glass cleaner.
  4. A rimmed glass tank sits directly on the stand, supported all the way around its frame, with no foam under it. A rimless or acrylic tank usually goes on a foam leveling mat. Follow the maker’s instructions.
  5. If the tank is second-hand, leak-test it first: fill it with plain water for 24 hours somewhere a leak can’t do damage, such as a garage floor, and check every seam.

Step 4: Rinse and add the substrate

Rinse gravel or sand in a bucket of tap water, pouring off the cloudy water until it runs mostly clear. Don’t rinse aquasoils unless the bag says to.

Substrate Depth Notes
Gravel, no live plants 1–2 in (2.5–5 cm) Easy to vacuum
Sand 1–2 in (2.5–5 cm) Best for corydoras and loaches
Any substrate with rooted plants 2–3 in (5–7.5 cm) Add root tabs to plain gravel or sand

The amount depends on the footprint, not the gallons. A 20 gallon long and a 29 gallon share a 30 × 12 in base, so both need about 20 lb (9 kg) of gravel or sand per inch of depth. That’s why the “1 lb per gallon” rule gives different depths in different tanks. The substrate calculator works from your tank’s length, width and target depth.

Step 5: Fit the filter and heater

Filter. For a typical community tank, choose a filter rated at about 4–6 times the tank volume per hour: 80–120 GPH (300–450 L/h) for a 20 gallon. For goldfish, large cichlids or a heavily stocked tank, aim for 6–10 times. Box ratings don’t allow for media, tubing or lift, so real flow is lower. Bettas and other long-finned fish need gentle flow, about 2–4 times, so use a sponge filter or one you can turn down. Fill a hang-on-back filter with water before plugging it in, or the pump can be damaged. Check your numbers with the filter flow calculator.

Heater. Makers’ charts and common rules of thumb range from about 2.5 to 5 watts per gallon (0.7–1.3 W per litre). The size you need depends on the gap between the coldest your room gets and the temperature your fish need, so size for winter nights, not a warm afternoon. Use the higher end for a cool room, a small tank or a tank without a lid. Above about 50 gallons, split the wattage between two heaters: one stuck-on heater is then less likely to overheat the tank, and if one fails the other keeps the water from chilling fast. Mount the heater near the filter outflow and put the thermometer at the far end. The heater size calculator uses your room and target temperatures.

Step 6: Add hardscape and plants

Push heavy rocks down through the substrate until they rest on the glass (or place them before the substrate), so digging fish can’t undermine and topple them. Soak new driftwood first, because it often floats and tints the water brown. To plant, fill the tank 4–6 in (10–15 cm) deep so plants are easier to place.

Step 7: Fill with treated water and switch on

  1. Pour room-temperature tap water onto a plate or clean bag so it doesn’t dig craters.
  2. Add water conditioner dosed for the whole tank, following the label. It neutralizes chlorine and chloramine within a few minutes. Letting water stand can clear chlorine, but not chloramine, so use conditioner every time.
  3. Fill to just below the rim and turn on the filter.
  4. Wait 20–30 minutes, then plug in the heater. Set it for the fish you planned: many community fish do well at about 76 °F (24 °C), but use the shared range from the stocking calculator.
  5. Fit the lid and set the light timer to about 5–6 hours a day at first, because new tanks grow algae easily. Work up to about 8 hours as plants start to grow.

Step 8: Run it for 24 hours and check

Next day, run a dry paper towel along every seam and under the tank. Any damp spot is a leak, so drain before it gets worse. Heater dials are often a few degrees off, so adjust until the thermometer holds your target. Give every power cord a drip loop, a dip below the socket so water drips off before reaching the plug.

Step 9: Cycle the tank before adding fish

Fish make ammonia, and nothing in a new tank breaks it down. Ammonia burns gills and gets more toxic as temperature and pH rise. Cycling grows bacteria that turn ammonia into nitrite (also toxic) and then into nitrate, which is much less harmful and leaves with water changes. University of Florida specialists put a new biofilter at six to eight weeks, and the Merck Veterinary Manual at up to 8 weeks; most home tanks take about 4–8 weeks.

The safest method is a fishless cycle:

  1. Dose pure ammonia (no scent or soap) to about 2 ppm. Products made for fishless cycling have a dose chart on the label; with household ammonia, add a little at a time and test. Rotting fish food also makes ammonia, but you can’t control the level, so use it only as a last resort.
  2. Test ammonia and nitrite every day or two. Add more ammonia only after the readings have dropped, not every day. If ammonia or nitrite climbs above about 5 ppm, stop dosing and do a water change, because very high levels slow the bacteria down.
  3. The tank has cycled when a 2 ppm dose reads 0 ppm ammonia and 0 ppm nitrite 24 hours later, with nitrate showing. Repeat the test the next day to confirm.
  4. Do one or two large water changes to bring nitrate under about 20 ppm, then add fish within a day or two so the bacteria keep their food supply.

Media from a healthy, disease-free tank speeds this up most. Bottled bacteria and lots of plants also help, but test before adding fish either way. Cloudy white water in the first week or two is usually a bacterial bloom and clears on its own. Our guide to cycling a fish tank has the day-by-day plan.

Step 10: Add fish slowly

  1. Start with a quarter to a third of your planned stock, choosing hardy, peaceful fish. In a tank of 20 gallons (76 L) or more, platies or cherry barbs make good first fish, and so do zebra danios in a tank at least 30 in (75 cm) long, such as a 20 gallon long.
  2. Feed a small pinch once a day for the first week.
  3. Test ammonia and nitrite every day or two. If either reads above 0, change 25–50% of the water and feed less. If fish gasp at the surface, stop eating or start dying, keep up the water changes and contact an aquatic vet.
  4. Wait about two weeks of zero readings before the next batch.
  5. Add territorial fish such as dwarf cichlids last. Sensitive grazers such as otocinclus do better once the tank has run a few months.

Acclimate each batch slowly, and if you can, quarantine new fish in a separate tank for 4–6 weeks first. If they get sick, follow the medication label exactly and ask an aquatic vet if you’re unsure what it is. Once fully stocked, change 25–30% of the water weekly and keep testing.

Equipment by tank size

Assumes a standard glass tank with a lid and tropical community fish. Heater sizes are what our heater calculator gives for water kept at 78 °F (26 °C) in a room that can drop to 65 °F (18 °C); a warmer room needs less. Filter flow is rated flow at 4–6 times the volume per hour; go higher for messy or crowded tanks. Gravel is a 2 in (5 cm) bed at about 100 lb per cubic foot (1.6 kg/L).

Tank Weight full Heater Filter flow Gravel, 2 in
10 gal (38 L) ~110 lb (50 kg) 50 W 40–60 GPH (150–230 L/h) ~23 lb (10 kg)
20 gal long (76 L) ~225 lb (102 kg) 75 W 80–120 GPH (300–450 L/h) ~42 lb (19 kg)
29 gal (110 L) ~330 lb (150 kg) 100 W 115–175 GPH (440–660 L/h) ~42 lb (19 kg)
40 gal breeder (151 L) ~460 lb (208 kg) 150 W 160–240 GPH (610–910 L/h) ~75 lb (34 kg)
55 gal (208 L) ~625 lb (284 kg) 2 × 100 W 220–330 GPH (830–1,250 L/h) ~72 lb (33 kg)
75 gal (284 L) ~850 lb (386 kg) 2 × 150 W 300–450 GPH (1,140–1,700 L/h) ~100 lb (45 kg)
125 gal (473 L) ~1,400 lb (635 kg) 2 × 250 W 500–750 GPH (1,890–2,840 L/h) ~150 lb (68 kg)

Full weights are a retailer’s approximate figures, and the retailer doesn’t say whether they include gravel. With the same 2 in gravel bed, our tank weight calculator, which also allows for glass thickness and an inch of air at the top, usually comes out about 5–20% lower, so treat the table as a safe upper estimate.

Common setup mistakes

Mistake What goes wrong Do this instead
Buying fish on impulse They outgrow the tank, fight or need another temperature Plan the whole stock before shopping
Rinsing filter media under the tap Chlorine and chloramine can kill much of the bacteria Rinse media in old tank water
No lid Jumpers such as zebra danios and hatchetfish land on the floor Fit a lid with tight cutouts
Overfeeding a new tank Uneaten food rots into ammonia Feed a small pinch once a day

Gear mentioned in this guide

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Frequently asked questions

How long after setting up a fish tank can you add fish?

When the tank has cycled, which usually takes about 4–8 weeks. Wait until ammonia and nitrite both read 0 ppm and nitrate shows on the test. Then start with a few hardy fish.

Can you put fish in a new tank the same day?

It's risky, because a new tank has no bacteria to break down waste and ammonia builds up within days. If you have to, add only one or two small hardy fish, use seeded filter media or a bottled bacteria product as its label directs, and test ammonia and nitrite every day. Change water the same day either shows any reading (0.25 ppm on most kits).

Do you need to rinse gravel before putting it in a fish tank?

Yes. Rinse gravel and sand in plain tap water, without soap, until the water runs mostly clear. Most aquasoils for planted tanks should not be rinsed, so check the bag.

What size fish tank is best for a beginner?

A 20 gallon long (76 L) or a 29 gallon (110 L). More water means temperature and water quality change more slowly, and there's room for a small community. A 10 gallon (38 L) works for nano fish but leaves less room for mistakes.

When should you turn on the heater in a new tank?

Turn the filter on as soon as the tank is full. Wait 20–30 minutes before plugging in the heater, so its glass can adjust to the water temperature. Never run a heater out of water, and unplug it before a water change.

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