I keep waffling back and forth on this. My main system is in a few tanks right now as I build my new fishroom. The old system was a 240, 75, 55 plumbed together with a 75 gal used as a sump. I am planning on the new system having the 240, a 125, 2x75 and the 55 plumbed together with a 46 gal as the sump. The plan for the sump is a place to plumb the skimmer to, and add doses and top off water. There will be a cryptic sump, and refigium plumbed to it as well. Thoughts