The flow rate through the sump and refugium of your aquarium should be very low. The low flow will help maximize the dwell time of the water in the protein skimmer, as well as the nutrient hungry algae that resides in the refugium. Some seasoned hobbyists suggest a flow through rate of about 4 times the aquarium volume. For example, a 90-gallon aquarium should have a return pump that puts out 360gph or less. To compensate for the decreased flow in the display tank, add more powerheads or swap out smaller pumps for larger ones. This will maintain adequate water flow in the tank, but also improved the filtering ability of your refugium and protein skimmer.