Agreed; make your sump as big as possible. Something along the lines of 40 gallons would be adequate, fit under the stand, and you'd have a decent size refugium. Then you should run the water level fairly low in the sump area to make sure you have enough capacity to hold the drainage from the tank when the power goes out. I made a nice sump/refugium combination for my old 100 gallon; I was able to get almost that much capacity and still leave room in the stand for my big skimmer, reactor, and 3 pumps. It was kind of cramped, but it fit. If I were doing it over I think I'd make the sump/refugium much larger and run the skimmer and reactor externally.