Don't mean to be a downer, but... I was at the coast a couple of weeks ago. I went snorkeling and found a medium size hermit crab. He made it back and was active in my tank. However, days later all my livestock started dropping off. I couldn't figure out if it was ick or something else. As a result, I lost a blue tang, dog face puffer, a pair of nice size saddleback clowns, a pair of percula, 2 gobies, 3 chromis, and various invertebrates. I took him out when I first started losing fish, but the others still died. The survivors include a six line wrasse, 3 chromis, a fox face, and a lawnmower blenny. I have various corals (mostly frags) and they are all doing fine. They may even be happier with all the livestock gone.
Anyhow, I'm not sure if the crab had anything to do with it, but it all happened when I put him in there. FYI.