Most problems in a new aquarium happen in the first six weeks, and almost all of them come from the same few mistakes: too many fish too soon, no cycled filter, and big swings in temperature or water chemistry. This checklist walks you through a setup that avoids them.
1. Choose the size and place first
A bigger tank is easier, not harder. More water dilutes waste and slows down every change in temperature and chemistry, so a 60–120 L tank is a far better first aquarium than a 20 L nano.
- Place it on a level, sturdy stand that can carry the full weight: water weighs 1 kg per liter, plus about 10% for glass, substrate and rock.
- Keep it out of direct sunlight and away from radiators, doors and windows.
- Leave space behind it for the filter, cables and a drip loop so water can’t run into the socket.
2. Pick the equipment
- Filter: rated for at least 4–5 times the tank volume per hour.
- Heater: for tropical fish, about 1 W per liter; a thermostat is essential.
- Light: on a timer, 6–8 hours a day to start.
- Test kit: liquid tests for ammonia, nitrite, nitrate, pH and KH/GH are more reliable than strips.
- Water conditioner: removes chlorine and chloramine from tap water.
3. Rinse, fill and plant
Rinse gravel or sand until the water runs clear (aqua soils are not rinsed). Add substrate, rock and wood, then fill slowly over a plate so the substrate isn’t stirred up. Plant as much as you can on day one: fast-growing plants use up waste and compete with algae.
Treat the water with conditioner, switch on the filter and heater, and check that the temperature settles where you want it.
4. Cycle the tank before adding fish
A new filter has no beneficial bacteria yet. Those bacteria are what turn toxic ammonia into nitrite and then into much safer nitrate. Building them up is called cycling and usually takes 3–6 weeks.
Read our guide to the nitrogen cycle for the full method. In short: add a small, steady source of ammonia, test every few days, and wait until ammonia and nitrite both read 0 with nitrate above 0.
5. Add fish slowly
Start with a few hardy fish, then wait two weeks and test before adding more. The bacteria colony grows with the waste it receives, so a sudden jump in fish load can cause an ammonia spike even in a cycled tank.
- Check that the species you choose suit your water hardness, temperature and tank size.
- Watch for schooling fish that need groups of 6–8 or more.
- If possible, keep new arrivals in a quarantine tank first.
6. Build a simple routine
- Test weekly for the first two months, then every one to two weeks.
- Change 20–30% of the water every week with conditioned water at the same temperature.
- Clean filter media in tank water, never under the tap, and never all of it at once.
Fishtify builds this routine for you: create your tank, add your livestock and it calculates target values, flags anything outside the safe range and reminds you when maintenance is due.