I am stocking up on equipment for my new 90g that I will be setting up in a month or two. I already have a few powerheads for my 37g, but I will clearly need more. I have read that I should have 35gph per gallon of the tank, so (35*90) 3150 gph of flow. I have not yet purchased a sump for this tank, but I was thinking that a 30g would be the largest that could comfortably fit in the stand, with room for the external iwaki and possibly a top off bucket. Getting back to the point, should I include the volume of the sump in this calculation? If so, I am guessing I should include the flow rate of the return pump. If I include the flow rate of the return pump, would it be reasonable to include the flow rate of the overflow? The flow rate of the overflow will be equal to the flow rate of the return pump..