I have about 1500gph in my tank, thats 50X turnover. I have a 250w MH 11" from the water surface. I never feed my blastos and they have grown from 5 polyps to about 18 in 8 months and are doing great. There is not direct flow at the colony, the flow bounces off the opposite side of the tank then hits the blastos so its pretty diffused, but still a lot of flow.