Time to buy a pump but I need some help

[WWWD]

Your kind of limited on your choices for pumps if you want to go submersible mag, sedra... The kicker is that submersible pumps for large sized tanks can be pretty loud and transfer heat into your water. I would suggest you reconsider how you have your sump setup and see if there is a way you can get an external pump in there somehow. Maybe even on a shelf or outside the stand.

[Johnny Reefer]

I use a Hagen Aquaclear 901/110 powerhead on my present 180g with 33g sump system. They push 900 gph at 0' head. My head is at 4' approx. (makes me sound short) so that calculates to about 750gph, if I remember correctly. But I have two 6" corner overflows, not just one, for a total of 24" linear overflow. You should determine how much gph your overflow can handle (there is a calculator on Reef Central), factor in the head, and then size your pump accordingly so it doesn't exceed the linear overflow capacity.

HTH,