make sure your nitrates are in check before adding any inverts. they(nitrates) tend to get a little high in fowlr tanks, with no ill effects on the fish. but, the inverts are far more sensitive to nitrates. i'd hate to see you lose a whole order of snails and crabs, or anything for that matter. there are some cool starfish available for FO tanks(or should i say non-reef tanks), like the african red-knob star, which looks similar to a chocolate chip star, only the "knobs" are red(you probably guessed that from the name, huh?).