How to set up your first aquarium: tank size, filter, heater and cycling

TUREFF• •0

The most common reason beginners lose fish is not the fish or the tank, but rushing. Fish go into water that looks clean but has no settled population of the bacteria that break down their waste. Setting up properly takes a few weeks, and almost all of that time is simply waiting for the tank to be ready.

Choosing a tank size

It sounds backwards, but a larger tank is often easier for a beginner than a tiny one. More water means temperature and water quality change more slowly, so small mistakes have less effect. A tank of moderate size gives a good choice of fish without being hard to maintain. Think about:

Weight: water is heavy, so a full tank needs a strong, level stand designed for it. Do not use ordinary furniture.
Position: away from direct sunlight (which drives algae) and radiators, near a power socket, and somewhere you will see it every day.
Access: you need room above and around it for maintenance.

The essential equipment

Filter: the most important piece. It moves water through media where the useful bacteria live. Choose one rated for at least the size of your tank.
Heater: needed for tropical fish. A heater with a thermostat, plus a separate thermometer so you can check it is working.
Lighting: for viewing and plants. A timer keeps the day length consistent.
Substrate: gravel or sand. Rinse it well first to remove dust. Choose sand if you plan bottom-dwellers with delicate barbels, and a plant substrate if you want a planted tank.
Water conditioner (dechlorinator): tap water often contains chlorine or chloramine, which harms fish and bacteria.
A test kit: to measure ammonia, nitrite, nitrate and pH. Liquid kits are generally considered more reliable than paper strips.
A lid or cover to stop fish jumping out and reduce evaporation.

The nitrogen cycle in plain terms

Fish produce ammonia, which is toxic. Bacteria that colonise the filter turn ammonia into nitrite, which is also toxic. A second group of bacteria turns nitrite into nitrate, which is much less harmful and is removed by regular water changes and taken up by plants. "Cycling" a tank means growing enough of these bacteria before the fish arrive.

Fishless cycling, step by step

Set up the tank, fill it with dechlorinated water and run the filter and heater.
Add a source of ammonia, such as pure ammonia made for the purpose or fish food left to break down. Follow the instructions of whatever method you choose and avoid overdosing.
Test the water every few days. Ammonia rises first, then falls as nitrite appears; later nitrite falls and nitrate rises.
Keep adding ammonia to feed the bacteria as the levels drop.
The tank is ready when it can turn a dose of ammonia into nitrate within about a day, with ammonia and nitrite both reading zero.
Do a large water change to bring nitrate down, then add a small number of fish.

A rough timeline

A fishless cycle commonly takes somewhere around three to six weeks, sometimes longer. Using filter media or gravel from an established, healthy tank can speed it up a lot. Bottled bacteria products may help, but test rather than trusting the label. Let the test kit, not the calendar, decide when you are ready.

After the cycle

Add fish gradually, a few at a time, so the bacteria can keep up.
Feed small amounts that are eaten within a couple of minutes.
Keep testing for the first few months.
Start a regular routine of partial water changes.

Setting up your first tank, or stuck mid-cycle? Post your test readings and questions in the comments and someone will help.