A small tank, set up slowly

Try this

1. Start bigger than you think. A 10 to 20 gallon freshwater tank is more stable than a tiny bowl, because small volumes change temperature and chemistry quickly.
2. Set up the tank without fish. Add substrate, a filter, a heater, rock or driftwood, and easy live plants. Fill it with dechlorinated water and let it run.
3. Cycle it first. Add a small source of ammonia and a bottle of beneficial bacteria, then test the water every few days. Over two to six weeks, ammonia and then nitrite rise and fall to zero as the bacteria take hold (API Fishcare).
4. Add a few fish, slowly. Choose small, hardy species that suit your tank, and add a few at a time so the bacteria can keep up.
5. Make maintenance a ritual. Feed lightly, test the water, and change about a quarter of it regularly. Ten minutes on a Sunday is enough.

If it feels hard

• If the water turns cloudy, a bacterial bloom is common in new tanks and usually clears on its own. Don’t add fish yet.
• If algae takes over, cut back the light hours and the feeding.
• If you are tempted by a reef tank, treat it as a later chapter. Saltwater and coral need more equipment and experience.

The science, briefly

Fish waste and leftover food release ammonia, which is toxic. One group of bacteria turns ammonia into nitrite, another turns nitrite into nitrate, which plants use and water changes remove. Cycling is simply growing those bacteria before fish depend on them. And watching the result is good for you: in a study at Britain’s National Marine Aquarium, people watching tanks showed better mood and lower heart rates (Prothom Alo).

Where to start

• How to cycle a new tank, step by step, from API Fishcare.
• A beginner’s guide to fishkeeping from the Calgary Aquarium Society.
• A smaller start: A forest in a jar.

Fill the tank. Wait for the water to be ready. Then sit and watch.