I have a drilled tank with sump and refug under the tank. I have a pool pump pumping the water back to tank. The problem I have is - I have to cut the flow on this pump way down or the one drain hole from the tank can not keep up. I changed to the biggest PVC I could use with the holes that are cut. Should I add a overflow box to increase flow to the sump or is it okay. The tank has plenty of flow inside with the Koralia magnum's. I just feel like I am not having the volume of water I would like going thru the sump and getting subjected to the skimmer etc.