I put two in my 135g for the same reason and they wiped it clean in about two weeks. And I mean clean. One of them has since gone on to that big reef tank in the sky, but my remaining Harlequin has not allowed the return of even one little white star since they ate them all. He also took about four days to devour a chocolate chip star that I put in there for him. It was about 1.5" arm to arm. He found it about 45 seconds after I put it in the tank and immediately flipped it over and starting macking down on it. He didn't stop until it was gone. I am sure he had some help from the snails, worms, and hermits, but man it was impressive to watch.