Before you start
- An aquarium and stand
- A filter (and heater for tropical fish)
- Substrate (gravel or sand) and decorations or live plants
- Water conditioner (dechlorinator)
- A water test kit
- A siphon and bucket used only for the tank
Method 1 Choose and set up the tank
Use drip loops on power cables so water can’t run down into sockets, and switch off equipment before putting your hands in the water.
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Step 1: Pick the size
Larger tanks are easier, because water conditions change more slowly. Around 60 litres (15 gallons) or more is a good beginner size. Avoid small bowls, which can’t hold a filter or stable water.
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Step 2: Find the right spot
Place the tank on a strong, level stand designed for the weight (water weighs about 1 kg per litre), away from direct sunlight, radiators and draughts, near a power socket.
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Step 3: Add substrate and decor
Rinse gravel or sand until the water runs clear, then add it with rocks, wood and plants. Use only aquarium-safe decorations.
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Step 4: Install equipment
Fit the filter and, for tropical fish, a heater set to the right temperature (many tropical fish like about 24–27°C). Add a thermometer and a lid and light.
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Step 5: Fill with treated water
Fill the tank, adding water conditioner to remove chlorine and chloramine from tap water, which harm fish and bacteria.
Why cycling matters
Fish waste and leftover food produce ammonia, which is toxic. Beneficial bacteria that grow in the filter turn ammonia into nitrite (also toxic) and then into nitrate, which is much less harmful and removed by water changes. A new tank has none of these bacteria, so fish added too soon can be poisoned (often called “new tank syndrome”). Growing the bacteria first is called cycling.
Method 2 Cycle the tank before adding fish
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Step 1: Run the filter
Run the filter and heater 24 hours a day from the start.
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Step 2: Add an ammonia source
For a fishless cycle, add a small amount of fish food or bottled aquarium ammonia, as the product instructions say, to feed the bacteria. Bottled beneficial bacteria can speed things up.
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Step 3: Test regularly
Test ammonia, nitrite and nitrate every few days. You’ll see ammonia rise and fall, then nitrite rise and fall, then nitrate appear.
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Step 4: Wait for the result
When ammonia and nitrite both read zero within 24 hours of adding ammonia, and nitrate is present, the tank is cycled. This usually takes 4–8 weeks. Do a large water change before adding fish.
Method 3 Add fish slowly
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Step 1: Choose compatible fish
Research adult size, temperament, water needs and group size. Hardy, peaceful beginner fish include many livebearers, tetras, corydoras catfish and rasboras, but always check they suit your tank.
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Step 2: Stock gradually
Add a few fish at a time, waiting 2–3 weeks between groups, so the bacteria can catch up.
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Step 3: Acclimatise
Float the sealed bag in the tank for about 15 minutes to match temperature, then add small amounts of tank water to the bag over 15–30 minutes. Net the fish into the tank and throw away the bag water.
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Step 4: Quarantine if possible
A separate quarantine tank for new fish prevents diseases spreading to your main tank.
Method 4 Look after the tank
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Step 1: Feed carefully
Feed once or twice a day only what the fish eat in about 2 minutes. Overfeeding is the most common cause of poor water quality.
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Step 2: Change water weekly
Siphon out 10–25% of the water each week, cleaning the gravel as you go, and replace it with conditioned water at a similar temperature.
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Step 3: Clean the filter gently
Rinse filter sponges in removed tank water, never tap water, and only when flow slows. Don’t replace all filter media at once, or you’ll lose the bacteria.
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Step 4: Keep testing
Test water weekly at first, then whenever fish behave oddly.
Troubleshooting
The water is cloudy
A milky cloud in a new tank is usually a bacterial bloom and clears on its own. Don’t overfeed, and avoid big cleanups while it settles.
Green algae everywhere
Reduce lighting to 6–8 hours a day, keep the tank out of sunlight, feed less and keep up with water changes.
A fish has white spots
This may be ich (white spot disease). Ask an aquatic shop or vet for a suitable treatment, and follow it carefully.
Frequently asked questions
Can I keep a goldfish in a bowl?
No. Goldfish grow large and produce lots of waste, so they need a big, filtered tank or pond.
How many fish can I keep?
It depends on the species’ adult size and needs, filtration and tank shape. Stock lightly and research each species.
Do I need a heater?
Tropical fish need one. Coldwater fish such as goldfish don’t, if the room stays at a stable temperature.
Summary
Choose a reasonably large tank, set up the filter, heater and substrate, and fill it with conditioned water. Cycle the tank for several weeks until ammonia and nitrite read zero, then add compatible fish a few at a time. Feed sparingly, change 10–25% of the water weekly, and test whenever something seems wrong.
