They are recommend for 55gal and up. I was thinking about one but I just read on another site that once they eat up the worms and Pods in the sand, unless its replentished they will die...
"It likes to eat Eats benthic sand crustaceans like spaghetti worms, tube worms, copepods, amphipods and other sandbed infauna"
"One Sand Sifting Sea Star can void a 5 inch sandbed in an 80 gallon system of living sandbed matter in just a few weeks. It will then proceed to stay hidden in the sand, starve to death and decay. Be sure to add this species to a well established tank with a lot of benthic invertebrates in the sand."