I had a sump/fuge built for my 75 and we pretty much measured out enough room for the skimmer in the first section, enough room for the return in the center section and left over was in the 3rd section for a fuge. Baffles are spaced about 1" apart and do a great job of keeping micro bubbles out of the return area. Overflow drains into both sides of the sump/fuge and both sides fill into the center which is shot back up via Mag 9.5 return pump. Its a little powerful so you could go down a size on the return if you wanted but its up to you. I've got mine diverted into the fuge area and use a ball valve to control flow into the tank. I hope you understand what I'm saying, if not email me and I can send pictures.