OK. I'm not exactly sure what a powerhead is. Marine depot doesn't have anything under their powerhead selection. I've been told i should maybe have 2 powerheads for my main tank. (75g Main tank, with 29g sump, (Aqua C Skimmer, rio pump for skimmer, and mag drive 9.5 for return pump)). I'm not even sure what a "powerhead" is or how it works or how to hook it up. I would like some help with this because I have made my list of all of my other equipment and would like help with this so i know what to get. Thanks.
(Also, tank is 75g 48" 18" 20" L W H)