hmm...a 2.5 could make for a really cool little tiny baby reef, but you really wouldn't be able to keep any fish, In my opinion. a 5.5 allows you to keep one little fish if you want to. A pretty cool little tank would be a 2.5 with a bunch of corals and a herd of sexy shrimp...the tank would be the perfect size to showcase those animals. Anyway...I don't think you'd notice that much of a difference work-wise between the two. It really comes down to what you want. I think a 5.5 is a perfect size for a
nano reef, but then again...my 5.5 doesn't look that great, so you can take my advice for what it's worth...I've been keeping reefs for a while, but I'm in no way an expert.
