Originally Posted by Stlrockguy
If I have 600 gallons per hour coming out how much am I needing to put back in
As much as you want with out going over that. The overflow will match your return pump up to the overflow's max flow.
If your return pump is pushing 400 gph
at the end of the plumbing then your overflow will empty your display at same rate. But if you pump is pushing 800 and overflow is rated at 600 you will be pushing more than it can handle and will overflow the display tank.