I've got 4 Hydor 425's plus the two factory return pumps in my 28 nano. The two in the bottom corners run full time, aimed a little bit inward toward the bottom of the rock work so there's no dead spots within the caves. The two at mid-level alternate on 2 minute cycles for good indirect cross current on the SPS (aimed straight forward into the curved glass), and the two returns run full time (266gph rated each).... that gives me 1807gph (64x) movement. Secret is getting everything positioned correctly so that the corals low front, primarily 'shrooms, aren't getting blown away. Just takes some playing around.....