What you need, and what it costs in time
Setting up the tank takes an afternoon. Getting it ready for fish takes four to eight weeks, because the filter has to grow the bacteria that make fish waste safe. That waiting period, the nitrogen cycle, is the step most beginners skip and the reason most first tanks lose fish. Plan for it from the start.
Equipment list:
- Tank, and a stand made for aquariums
- Filter
- Heater and thermometer (for tropical fish)
- Substrate: gravel or sand
- Light and lid
- Water conditioner (dechlorinator)
- Liquid test kit for ammonia, nitrite, nitrate and pH
- A bucket and a gravel vacuum used only for the tank
- A source of ammonia for cycling (see step 7)
Step 1: Choose the biggest tank you have room for
Bigger tanks are easier, not harder. More water dilutes mistakes: a missed water change or a little overfeeding barely registers in 30 gallons and can be an emergency in 5.
A 20-gallon long or a 29-gallon tank (75–110 litres) is the best first size: stable, affordable, and big enough for a proper community of small fish. If space is tight, 10 gallons (38 L) is the smallest sensible tank for a small group of fish, and 5 gallons (19 L) suits a single betta.
Use the dimensions calculator to see which standard sizes fit your space.
Step 2: Pick the place
A filled tank is heavy: about 10 to 12 lb per gallon with its stand, so a 29-gallon tank weighs around 350 lb (160 kg). Check it with the weight calculator. Choose a spot that is:
- On a level, solid floor, on a stand built for the load
- Out of direct sunlight, which overheats the water and feeds algae
- Away from radiators, heaters and draughty doors
- Near a power socket, and within reach of a tap or easy bucket route
Step 3: Rinse and add the substrate
Rinse gravel or sand in a bucket until the water runs clear. Aim for 4–5 cm (1.5–2 in) of gravel or 2.5–4 cm of sand: the substrate calculator tells you how many bags that is. Slope it slightly up towards the back.
Step 4: Fit the filter and heater
Choose a filter rated to turn the tank's volume over 4 to 6 times an hour: 120–180 GPH for a 29-gallon tank. The filter calculator gives your figure. For the heater, allow about 5 watts per gallon in a normal room: 150 W for 29 gallons. Check yours with the heater calculator.
Fit both, but do not plug them in yet. Heaters must be under water before they are switched on.
Step 5: Add decor and fill
Place rocks, wood and any plants. Put a plate on the substrate and pour water onto it so the bed is not disturbed. Fill to about 2–3 cm below the rim. Add water conditioner for the full tank volume: it removes the chlorine or chloramine that tap water carries, which would otherwise kill the filter bacteria and the fish.
Step 6: Switch on and check
Plug in the filter, heater and light. Over the next day:
- Check the temperature settles where you want it: 24–26 °C (75–79 °F) for most tropical fish
- Check for leaks around the base
- Top up if the filter needed water to prime
Cloudy water in the first days is normal and clears on its own.
Step 7: Cycle the tank before adding fish
Fish produce ammonia, which is poisonous. Bacteria in the filter turn ammonia into nitrite (also poisonous), and other bacteria turn nitrite into nitrate (safe in moderate amounts, and removed by water changes). A new filter has none of these bacteria.
To grow them without harming fish, do a fishless cycle: add a little ammonia every day or two to feed the bacteria, and test the water. The tank is ready when it can clear 2 ppm of ammonia to zero ammonia and zero nitrite within 24 hours. Our nitrogen cycle guide gives the full day-by-day method.
Step 8: Add fish slowly
When the cycle is complete, do a large water change to bring nitrate under 20 ppm, then add your first fish: a small group, not the whole list. Add more every week or two, testing for ammonia and nitrite as you go. Both should stay at zero.
Plan the full stock before you buy anything, with the stocking calculator. It shows how full the tank will be at adult size and flags fish that will not get along. Good first fish for a 20–29 gallon tank include harlequin rasboras, cherry barbs, platies, corydoras catfish and honey gouramis.
To bring fish home safely: float the sealed bag in the tank for 15–20 minutes to match the temperature, then add small amounts of tank water to the bag over another 15–20 minutes, and net the fish into the tank. Do not pour the shop water in.
Step 9: The weekly routine
- Daily: feed once or twice, only what is eaten in a couple of minutes. Look at every fish.
- Weekly: change 25–50% of the water with conditioned water at tank temperature, and vacuum the substrate. The water change calculator finds the right amount for your tank.
- Monthly: rinse the filter media in a bucket of tank water (never under the tap). Test nitrate.
That routine, kept up, is nearly all there is to keeping fish well.
Questions and answers
How long should a new tank run before adding fish?
Until the nitrogen cycle is complete, which usually takes four to eight weeks. Running an empty tank for a day or a week does nothing unless you are feeding the filter bacteria with ammonia and testing the water.
What is the best size tank for a beginner?
A 20-gallon long or 29-gallon tank (75–110 litres). They are large enough to be stable and forgiving, and small enough to fit most rooms and budgets.
Can I put fish in the same day I set up the tank?
Not safely. Without filter bacteria, ammonia from the fish builds up within days. If you already have fish in a new tank, test daily and change water whenever ammonia or nitrite reads above zero.
Do I need a heater?
For tropical fish and bettas, yes, unless your room stays at 24 °C (75 °F) or more day and night all year. Goldfish and White Cloud minnows do not need one in a normal home.