I have kept a pincushion and a pencil urchin in a reef tank. They are very good grazers but will knock down and pickup any frag that is not well secured.
I have a purple urchin. It comes out at night to graze. It knocks over rock work. They poop alot, but don't mess with corals. I like mine, its been in the tank two years.
I prefer long spine black urchins, until they get too big. They do grow very fast.
But i find them to be pretty cool, very active, and the least destructive, even though you might think the opposite with those long spines.
Just be careful when reaching into your tank.
I have a short spine black urchin, he's a model citizen though I think he eats all my coraline. He doesn't carry anything around and doesn't sting too much when I clumsily impale my finger on a spine..
I have a 2 pencil urchins in my 20g, they are very cool. I got them tiny and might have to give them away because once big they get strong and could knock over rocks that aren't placed well. It's not likely but can happen.
I had an urchin collection business here in New York for a few years and have had urchins in my tank for about 40 years. No problem except for that knocking over stuff.
They are very good grazers but will knock down and pickup any frag that is not well secured.
I have a number of Brown Short Spines in my tank. Never had a problem but the to like to carry stuff around with them. I added several small pincushions about a month ago and so far they are all doing fine. Although one did get eating by my starfish.:cry:
I did have a pencil urchin who looked real cool but he munched on too many of my corals so I thru him in the sump. Unfortunately, he was promptly eating by the stone crab :squigglemouth:
I have always liked long spine urchins and tuxedo urchins .... never have had a problem, but the tux does sometimes like to relocate small rocks and frags
I was never really an urchin fan, until a conversation with someone convinced me to have one.
I like the tuxedo urchins as they have shorter spines and aren't completely a bulldozer.
My favorite urchin was my Halloween Urchin, but I ended up removing him from my reef tank as I was frustrated with its determination to pick up and move any small frags and drop them behind the aquascaping.