I have a 240 gallon mixed reef aquarium. I have a big SWC 250 Xtreme skimmer and a 75 gallon sump/fuge with plenty of macro in it. I don't over feed and I still have surface scum, I will admit my powerheads don't stir up the water surface that much, but I am afraid to move them and mess up the flow that everything is thriving under.