I was looking at HOBs today, and it seems that even with two of them rated for a 75 gallon tank, they would be hard pressed to keep up with a desirable turn over rate. From an equation I found in these forums, it appears a 55 tank with the dimensions of 48 by 12.5 by 21 would need around 530 gph. Please correct me if I'm wrong about my calculations. Most of the HOBs I found barley push it at 300 gph. I understand running one at each end of the tank would be ideal in this situation but I really feel myself leaning toward a sump because of all the wires I would have hanging around from such a set up. At least with a sump, I would be able to also hide the heater. But the big question is how much power would I need to get the water from the sump back into the tank at around 500 gph? Or is this over kill?