<a href=showthread.php?s=&postid=13808547#post13808547 target=_blank>Originally posted</a> by wpecoul
I don't have a system set-up like the one you are wanting advice on, but I've seen enough and help built enough. If I may offer a few points...
1. I don't know how big your skimmer is, but four compartments on a 4-foot sump is pushing it. I would go with three - skimmer on one side, refugium on the other and return in the middle. Ideally, you don't want to skim water before the refugium section, and you definitely don't want to make your tank-friendly refugium escapees have to go past any sort of mechanical filtration to get to the return pump. Also, I'd reconsider using a 55G tank - one foot depth (front to back) isn't much to work with.
2. Drop one drain straight to the section with the skimmer. Take the other drain down, tee it with one line going to the skimmer section, and the other line(with a valve) down into the the refugium side. That way you can limit the water into the refugium but still give a free outlet to the remaining drain water (over to the skimmer).
3. Feed any carbon or phosphate reactors from the skimmer section with a maxijet or similar. Hang them on the back side of the sump and have the outflow routed into the center (return) section.
4. Put a three-sheet baffle on the skimmer side of the return section, but a single baffle (cut into a weir) on the refugium side.
5. If you know you want an external return, I'd suggest a true external pump. The big Mags run really, really hot when run externally. If you can afford it, I'd suggest two return pumps - if one quits, you are not looking around for a paddle.
6 and last - unless you are going to change the socks every 2-3 days without fail, I wouldn't use them.
Hope this helps,
Will (the Montgomery one)