Hrm. I am effectively running a closed loop, it seems, unless I'm missing something important. Water runs from my overflow to my sump, thru some filter media, hits the skimmer, and then passes a polyfilter to a 650gph mag when it is pumped up thru a pipe that is connected to our plenum frame with a pair of pipes rising up thru the 5+" sand bed, and as far as I can tell, even without the powerheads on, I don't really have any dead-spots, but water-flow is not, in my opinion, excessive in any part of the tank either. Sad for me, however, I have a lot of detritus in the tank that seems to be too much for - or even beyond - the abilities of my current cleanup crew. Additionally, my diamond watchman goby stirs up a lot of sand, and much of that detritus winds up on the rock.. and, well, even as often as I dust, no matter how I angle the power-head flow at my overflow, I just can't seem to get enough of the crud out fast enough, and I'm wary of introducing too much livestock too quickly, esp. now that I plan to start QT'ing most everything. Oh well, I guess water changes will have to continue to be the answer... Yarrr.