Setting up your first aquarium

Fish keeping is often sold as the easy option, but fish depend entirely on the water you give them. The good news is that a well-planned tank is not difficult to look after, and a patient start prevents most of the problems beginners run into.

This guide follows the order you would actually set up a tank in, from choosing equipment to adding your first fish, and ends with a simple care routine.

Why a bowl is a poor choice

The classic goldfish bowl is one of the hardest homes to keep healthy. A small volume of water gets dirty and changes temperature quickly, there is rarely room for a proper filter or heater, and the curved glass leaves little surface area for oxygen to enter the water. Most fish need a filtered, appropriately sized tank, and some, such as goldfish, grow much larger than people expect.

Choosing a tank size

It sounds backwards, but a slightly larger tank is often easier for a beginner than a very small one. More water dilutes waste and buffers sudden changes in temperature and chemistry, which gives you more time to notice and fix a problem. Choose the size around the adult fish you want to keep, check that your floor or furniture can carry the full weight of water, glass and gravel.

The essential equipment

• Filter: keeps water moving and, more importantly, houses the beneficial bacteria that break down waste. Choose one rated for your tank size.
• Heater: needed for tropical fish, which require stable warm water. A heater with a built-in thermostat and a separate thermometer makes checking easy.
• Lighting: gives a day and night rhythm and helps live plants grow. A timer keeps it regular; too much light can encourage algae.
• Substrate: gravel or sand on the bottom, chosen to suit the fish and plants you plan to keep.
• Plants and decor: live plants use up some waste and give fish cover. Add hiding places such as caves or driftwood, with no sharp edges.
• Lid or cover: many fish can jump, and a cover also reduces evaporation.
• Water conditioner: tap water is often treated with chlorine or chloramine, which harm fish, so a dechlorinator is usually needed.

The nitrogen cycle, explained simply

Fish produce waste, and uneaten food and dead plant matter rot. All of this releases ammonia, which is toxic to fish. In a healthy tank, one group of bacteria turns ammonia into nitrite, which is also toxic, and another group turns nitrite into nitrate, which is far less harmful in moderate amounts. Nitrate is then kept low through partial water changes and plants.

A brand new tank has none of these bacteria yet. They grow slowly, mainly in the filter, and building up a large enough colony is called cycling the tank.

Cycling before adding fish

1. Set up the tank, fill it with conditioned water and run the filter and heater.
2. Provide a small, steady source of ammonia, following the instructions of the product or your aquarium shop.
3. Test the water every few days. You should see ammonia rise and fall, then nitrite rise and fall, while nitrate appears.
4. The tank is generally considered cycled when ammonia and nitrite stay at zero and nitrate is present.
5. Only then add a few fish, and keep testing.

Water testing kits

You cannot see ammonia or nitrite, so a test kit is your window into the tank. Liquid test kits covering ammonia, nitrite, nitrate and pH are widely regarded as more reliable than strips, though strips are handy for quick checks.

Choosing compatible beginner fish

• Research adult size: some fish sold small grow far too big for home aquariums.
• Match water needs: keep species together that like similar temperature and water conditions.
• Check temperament: avoid mixing fin-nippers with slow, long-finned fish, or large fish with ones small enough to be eaten.
• Respect social needs: many small fish feel safe only in a group of their own kind, while some species must be kept alone.
• Ask questions: a good aquarium shop will happily explain the needs of each species and talk you out of poor combinations.

Add fish a few at a time, with gaps of a couple of weeks or more between additions, so the bacteria can keep up with the extra waste. Quarantining new fish in a separate tank, where possible, reduces the risk of bringing in disease.

Feeding sparingly

Overfeeding is one of the easiest ways to pollute a tank. Offer a small amount of food that suits the species and is eaten quickly, and remove anything left over. Healthy adult fish generally cope well with a missed meal; they do not cope well with dirty water.

Weekly partial water changes

Even with a good filter, nitrate and other waste build up over time. Regular partial water changes, typically every week or so, remove some of this and refresh minerals. Use conditioned water at a similar temperature, and clean the substrate with a gravel siphon as you go. Rinse filter media in removed tank water rather than tap water, so you do not wash away the beneficial bacteria. Your test results and your shop or vet can help you judge how much to change for your setup.

Signs of trouble

• Gasping at the surface or rapid gill movement.
• Clamped fins, hiding much more than usual or lying on the bottom.
• White spots, fuzzy patches, frayed fins or cloudy eyes.
• Loss of appetite, swimming erratically or rubbing against objects.
• Sudden cloudy or foul-smelling water.

Daily and weekly checklist

• Every day: feed a small amount, check that every fish is active and eating, and glance at the thermometer and filter.
• Every week: test the water, do a partial water change and siphon the substrate.
• Every week: wipe algae from the glass and trim plants as needed.
• Every few weeks: rinse filter media gently in tank water, never replacing it all at once.