I'm setting up a 40g breeder as a mixed reef tank. Looking for what powerheads would work best in the tank. I want 2 so that I can create a bit of turbulence in the water, but not overpower the corals. What is recommended here as far as brands to buy, and brands to avoid? And how do I calculate how much gph I'm going to need? I plan on starting with some inverts and live rock/sand, maybe add some clownfish as well.