54gal, and the sump would be 10gal, but I'd like to incorporate my old 20gal into the sump as well. Max 90gal system total. And if you're running it on a 125 or 150 i'm sure it'd be great for my little tank. I am planning on maxing out my tank on fish and coral, so i'm not sure how that would effect things, but i'd like to also fill the 10gal up with rock, and then divide the 20gal between skimmer and fuge. I have an HOB fuge now that is totally loaded with pods, so i'm reluctant to take everything out and put it in a sump tank. I guess we will see when the time comes