I just wanted to add that I have 2 purple urchins (common urchins) in my tank, that I sorta wish I never acquired. Mine loves leather corals, and I see him all the time perched up on top of my frag, rasping away at it. When he gets off, there is a nice little white spot on the top of it. I've also noticed it cruising through my yellow polyps and zoos. My tank is practically devoid of coraline algae, and unless I triple epoxy something to the rock, it's coming off beause of my klutzy urchins. The other night, I found it chugging away over my new ricordea polyp.
So my advice, stay away from the purple urchins. And if anybody has a FOWLR
tank and wants one, just let me know. lol.
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