if you built your sump I'm sure you have done your homework, but on an off chance - - you should be able to return 1/3 more water to the tank as the overflow box is able to send to the sump [ i.e. box is capable of 100 gph, return pump should be able to put out 130gph mnimum]- -a tee valve {similar to the adjustment on a skimmer or HOB filter will allow you to "equallize" sump fill and tank return - -the output from the adjusted side of the valve can have a bag full of carbon put on it for water polishing {might as well use everything right?, lol Boss