I don't know.. Fish that feed on the water column feed on plankton.. Plankton in our refugium's is precisely what we want to get into our tank, isn't it? By putting a fish in your refugium tank, you're kind of ruining the definition of a "refugium". If anything, I would opt for a Herbivore or something along those lines, however there aren't many small one's of those. A lobster, crab, pistol shrimp might make a decent addition, but I wouldn't put any fish in there...
- Mac