Thought I,d refrase that

[john5555leonard]

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

[Airlite]

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?

[john5555leonard]

No not pump fed , Gravity fed and pump return ,

[Manky Sanke]

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.