do you mean undergravel filter (ugf)? are you keeping a planted or fish only tank?
ugf has a similar function with a canister filter, that is, to provide biological filtration. the gravel provides a media for bacteria to colonise.
for planted tank, you do not need ugf. if you have base fertilizer, using ugf will cause nutrients to be ‘pulled’ into the water column. using a canister filter is fine with a flow rate of 2-3x your tank volume.
you can use those bottled bacteria cultures to kick start the bacteria colony in your canister filter. if you have access to a mature tank, grab a handful of the gravel and dump into you tank. this will do as well.








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