I was looking into getting a long spine sea urchin. I inquired and the guy folowed up after our initial talk and I bought one today. But its basketball size. And my tank is a 120 4x2 base. So I panicked and took him to the fish store to trade him. The offered to take him for free which I could not do. So I brough him home. In the tank is a 5" Grouper and two 12" Eels. I think it could work and hope it will but I am not sure. I meaning I am worried about the fish and eels getting stung.