I have one in my tank, but in order to do anygood, according to saltwaterfish.com you need one for every few square inches of sandspace. My one hasn't done crap for nitrates, lol. but I got him just cause I wanted a cool, non photosynthetic clam in the tank. Oh, and if you are thinking about getting one, keep in mind that you'll never see the bugger. diggs down about 3-4 inches into the sandbed and at most you may see it's mouth or "other end" sticking up out of the substrate. it's still cool to have one though, lol.