Red Dragon;
Sounds like a cyano outbreak. It's definitely associated with areas of low flow that allow the algae/bacteria to accumulate. Actually, usually blue legged hermits and typical snails (astrea/turbo) usually don't eat the stuff. I've heard fighting conch will eat it. You can also try a diadema (long spined) urchin. Shimek says these are the best 2 herbivores available for reef tanks. Hermits are scavengers that will eat whatever they can catch. Definitely avoid the pencil urchin. I saw a diadema urchin at fintique today; try that.