Want a sea urchin...Can I keep it?

[Burrito1]

I have a 20 gallon tank with one sps, candy cane, brain coral, GSP, and several softies, all of the coral is relatively small. The tank has been set up since Oct. 07 and I have about 20 pounds of rock and several species of macro-algae. Oh, and a clownfish, six-line wrasse, mandarin (He is a fatty), and a firefish. Question is, will the sea urchin completely strip the tank and rocks of color? I was thinking of tuxedo sea urchin.....

 

[fungia]

urchins eat all algae, even coralline. so in a smaller tank like your tank the urchin might strip out the rocks quickly. my pin urchin leaves marks where it goes, you can see a trail of bare rock. and they are clumsy and sometimes munch on corals or knock stuff over so be careful.