i once read an article that said, "once you think that you have enough water movement, double it." I don't how true this is but i'm pretty sure the more the merrier. I currently have a 46 bow FOWLR with two 1140 peguin p/h's, 1 in each corner pushing about 300 gph and then 2 mini p/h's in the middle pushing 150 each. i figured this was enough for me.