I have just started my first saltwater tank. It is a 55g with live rock. I want to make it a reef tank with inverts. I have read that many corals, etc. need good water movement. My question is this - should the powerhead(s) be placed at the surface of the tank? or should it be placed down in the middle of the tank where the flow can be directed over the rock? or one of each? My powerhead is an AquaClear 50 (~270 gph, I think). Also, using a Penguin 200 Biowheel Filter. I know that different corals want different amounts of flow. Second question is about lighting. I have flourescents, which are normal output, I think. I currently have a 40w actinic, a 40w 6700k daylight, and a 15w 18,000k and another 15w daylight. I'm wondering if this is going to be enough. I know it probably depends on what I'm trying to grow. Thanks.