Your pump should be able to handle 25% of your fish tank volume per hour, at the head height you need.

For example, if you have a 1000L fish tank that is 1.5meters below the top of the biofilter, you will need a pump with a flow rate of 1000L/p/h at a head height of 1.5m.

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BarryT Selected answer as best 11 January 2024