20g should work nice for the sump Melevsreef.com - DIY Glass Sump & Refugium is always a goos referance when putting a sump together what skimmer u guna go with?
I lucked out and am buying a month old 1250 gph Blueline pump and the guy is throwing in the 20 gallon acrylic sump with it. This weekend I'm going to fill it up with RO and make sure everything is sound and run the sump. I have 40 lbs of ultra premium live rock waiting for me and at guys house I buy aquarium stuff from. Another 20 lbs of rock from one of my Aquapods. I'll probably put about 20 lbs of lace rock or something in there to on top of white sand. It's going to look great.