it depends on the size of the QT and the size of the bio-wheel. Also if it's hang on back or if it's a canister/hob
. For example I use the Magnum Hot which is a hob
but has it's own outlet similar to a ph and it puts out 250 gph
which is enough for my 20 gal
QT for circulation/oxygenation purposes. If you aren't moving at least 10 times tank volume then I'd get a ph.