Simply Koi and More Koi

If you had a set of bays fed by 1 4 inch pipe from a bottom drain what size (Gph ) would you use for the return , thanks John

John, did you say in another thread that your filter is pump fed from the bd via the 4" pipe or are you gravity fed to the filter and use a pump to return?

No not pump fed , Gravity fed and pump return ,

Sorry missed this one. The flow rate through a filter ideally should be enough to give the pond at least a one hour turnover so the pump flow rate should sufficient to achieve this after friction losses and head losses are taken into account.