i have a yellow not a green.
i have also not had any problem with him or the one before nibbling on any corals.
they are great fish. very friendly. mine begs for food and mostly hangs out on the glass. never hides even when my hand is in in the tank or I'm siphoning
but
they can be a pain to get to eat. make sure you find one that does not have a pinched belly. if possible, ask to see them eat and choose one that eats the food.
they also need good quality food. otherwise they get these skin ulcers. I've seen it a few times. I feed mine a both flake and a prepared frozen food called limpits. you can use cyclopeze to get them to start eating sometimes, but they are fussy and do sometimes starve.