I have a thorny oyster about 4'' round (more the size of a large orange) and I wished I gave more thought before buying it. Got at LFS, who only had the one. I'm trying to fight a hair algae problem in a tank I want to keep coral and trying to keep it fed at the same time, -difficult. Especially since I don't know how to tell if it's getting enough food or slowly dying. I'm currently trying to set up a seperate tank for animals who like "dirtier" water. Don't mean to jump on this thread but just how do you know they aren't starving?