urchins are tricky, some are very reef safe, some not so much, I have a pink pincushion urchin and a red pencil urchin, the pincushion (a lolt like a tuxedo) is like a cow that never stops moving, he takes care of alot of algae coralline if im not careful.. the pencil urchin which looks soo cool to me is more of meat eater, he east algae too but I caught hime eating a candycane coral that I was rehabbing...im guessing b/c It was 3/4 dead and on the rebound. i actually spot feed mine algae from a shet of dried red algae. you can get so colupra or some otherlive good algae for them to eat so they stay off of what you want. But if he has already taken some of your corals out, expect it to happen again...Id actually see if I could trade him in on something from a LFS
, you dont want him eating all of your algae in your sump..