I have one in a 20ish gal and it has never bothered a coral yet. It picks minute algae pieces of off the rocks and also eats bubble algae (bless his heart
).
I think the key is getting a true emerald crab. I heard once that there are something like 17 different species of crab that are all sold at lfs's under the name "emerald crab". As far as I understand, the key is in flattened saucer-shaped claw tips instead of pointed claw tips. Of course, you always take the risk of an animal going rogue and behaving in the worst way it possibly could. I have bought two emerald crabs from Wai's and had really good success each time.
- Chad