How do I set up a first fish tank?

Almost every failed first aquarium fails for the same reason, and it is not neglect. Fish produce ammonia, which is acutely toxic. In an established tank, bacteria in the filter convert it to nitrite, which is also toxic, and other bacteria convert that to relatively harmless nitrate removed by water changes. Those bacterial colonies take weeks to establish. Put fish into a new tank and they swim in their own ammonia while the colony catches up — which is what "new tank syndrome" is.

Safety

Step by step

1. Buy the largest tank you can accommodate.Water chemistry in a large volume changes slowly, which is forgiving. A small tank swings quickly and punishes small errors. Very small tanks and bowls are the hardest possible starting point despite being sold as beginner options.
2. Work out the weight and where it will stand.Roughly one kilogram per litre of water, plus tank, substrate and decoration. Use a purpose-made stand or furniture rated for the load, on a solid floor, level, and away from direct sunlight and radiators.
3. Choose the fish before the tank is set up, not after.Adult size, temperature range, water hardness, whether they shoal, and whether they are compatible. A great many beginner problems are a fish that grows to thirty centimetres in a tank sold as suitable for it. Research from a source that is not selling you the fish.
4. Install substrate, filter, heater and lighting.Rinse substrate thoroughly with water only. A filter rated for at least the tank volume, a heater with a thermostat for tropical species, and a light on a timer. Keep all cables on a drip loop below the socket.
5. Fill with dechlorinated water.Tap water contains chlorine or chloramine, which kills the filter bacteria you are about to grow as well as harming fish. Use a dechlorinator every time you add tap water, including for water changes, for the life of the tank.
6. Cycle the filter before adding fish.Add a source of ammonia — bottled pure ammonia is the controlled method — and test daily. Ammonia rises then falls as nitrite appears; nitrite rises then falls as nitrate appears. When ammonia and nitrite both read zero within a day of dosing, the filter is cycled. Expect several weeks.
7. Buy a liquid test kit, not strips.You need ammonia, nitrite, nitrate and pH. Liquid reagent kits are considerably more accurate than paper strips, and during cycling the readings are the entire point.
8. Seed the filter if you can.Mature filter media, a sponge or gravel from an established healthy tank shortens cycling dramatically. Bottled bacteria products vary in effectiveness. Never rush a cycle by adding fish.
9. Add fish slowly and in the right order.A small number of hardy fish first, then wait a fortnight and test before adding more. Each addition increases the load and the filter needs time to catch up. Float the bag to equalise temperature, then acclimatise gradually to the tank water.
10. Establish the weekly routine.A partial water change of around a quarter to a third, using dechlorinated water at matched temperature, with the substrate vacuumed. Rinse filter media in old tank water, never under the tap — chlorine kills the colony and restarts the cycle.
11. Feed far less than you expect to.What the fish clear in a couple of minutes, once a day. Overfeeding is the commonest single mistake: uneaten food rots and produces ammonia, which is the problem you spent weeks preparing for.

Common mistakes

• Adding fish on the day the tank is filled — There are no filter bacteria yet, so ammonia accumulates. This is the single most common cause of a failed first tank.
• Rinsing filter media under the tap — Chlorine kills the bacterial colony and the tank effectively starts cycling again, with fish in it. Rinse in tank water taken out during a water change.
• Buying a very small tank because it seems easier — Small volumes swing rapidly in temperature and chemistry. A larger tank is genuinely more forgiving.

Questions people ask