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Aquarium tool

Heater and filter calculator

Size a heater and a filter for your tank.

The fish are

Gentle flow suits bettas, discus, shrimp and fancy goldfish. Big or messy eaters include goldfish, oscars and large cichlids.

Enter your tank's water volume to begin.

About these figures

These are common rules of thumb: 4 to 5 tank volumes an hour for ordinary fish, 2 to 3 for gentle flow and 6 to 10 for messy ones, and more watts for each degree the room is below your target. They are a starting point, not a guarantee.

Where the figures come from

These are common rules of thumb, not maker data. A heater needs more watts per litre the colder your room is compared with the temperature you want. A filter should move 4 to 5 tank volumes of water an hour for ordinary fish, 2 to 3 for fish that want gentle flow, and 6 to 10 for big or messy ones.

Check it yourself

Always confirm the real temperature with a thermometer, and check the maker’s own guidance for your tank size.

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