I *think* one of the smaller wrasses such as a 6line wrasse or a fairy wrasse (note not all fairy wrasses are equal - some do get larger than others, so check what species you'd like). The two downsides, 6lines do tend to get cranky as they age (mine killed a mandarin
), and fairy wrasses jump. In fact, I would suggest do not *ever* put a fairy wrasse into an open top tank, and make sure that the canopy is enclosed well enough that when they *do* jump, they get bounced back into the tank. If you have a cross brace in the tank I'd even think twice about it. Eurobracing should be OK though since they'll likely just flop about until they fall in again. I lost a pair (both fish of the pair) one night because the hood hatch was left open after feeding.
