return pump size?

[Myka]

You WILL have to add a powerhead(s). The only way you can potentially eliminate powerheads is if you create a closed loop, which essentially works like and external powerhead. It doesn't run through the sump. You need the powerhead(s) to keep detritus from settling on the sand, as well many corals need the extra flow. When you find a nook where the detritus settles you need to adjust your powerhead(s) or get another one.

I have a 33g setup currently and I'm running a MaxiJet 1200 for circulation. I also have an AquaClear 500 (has rubble in it, and a sack of carbon every once in awhile), and a Remora skimmer which is powered by a MJ1200 as well adding to the flow. It also has a MJ400 running a PhosBan Reactor, but it's dialed back so far it hardly counts. My tank could use a touch more flow, but it's getting pretty cluttered. As least with the sump you will be able to eliminate a lot of the stuff I have to put right in the tank like the skimmer, reactor, heater, and you could put the carbon in the sump instead of an AquaClear. Can't wait for my new tank (with sump!) to be ready!