I had a 10g refuge under my 10g display, mainly to see if I could do it. But what i found is that keeping two ocellaris (and a purple firefish for a while), it really wasn't needed. Let's face it, a 10g nano basically IS IT'S OWN REFUGE. You'll have, what, 20+lbs of LR and 20lbs of live sand in a 10g?........what i concluded, besides the way I set up the refuge filtering down from an AC 150 and returning with a regulated PH was assinine, was that there was no beneficial effect of having a 10g refuge under a 10g tank. Prior to hooking up the system, i had no measurable nitrates, nitrites, or ammonia.....and after, I saw no sign of possitive effect on my LPS. I believe the REAL furthering of nanos will be in the design and build of skimmers accomodating 10-20g tanks.