As long as I can get my vertex 180i out of the sump I'll be using a 55 gal under the 125 Im setting up. I believe that to be the biggest that will fit in that space? I currently have my return tee'd off to feed my refugium on my 75, would it be better to keep this configuration or tee off a drain to feed unskimmed water into the fuge? There will just be some live rock and chaeto mostly to grow pods and some nutrient export. Also if any one has any tips or pics of preferred designs feel free to share. As of now I'll do drain and skimmer, middle for return and far end for fuge