I have a small tank, that just has a large maroon clown and a anemone in it no coral or any thing because the clown just pushes them around the tank, he is a bully, so i have caught the urchin and put him in thereYep, I have two of the rock boring urchin type and they do get stuck into the coralline algae. They only come out at night. If you decide to keep it you'll be able to get it back out later by searching for it well after dark and plucking it out.