The earlier you attack this problem, the easier it will be to remove the ring. A thorough cleaning with a commercial acid-based bowl cleaner may do the trick. If the bowl cleaner doesn't work, try using a green, nylon-backed scrub sponge along with the acid. For an old ring, use a pumice stone. Wet the stone with the water in the bowl and rub it on the ringKeep the stone wet the entire time you're scrubbing. Pumice stones should only be used on vitreous china toilets - never on colored, enamel or plastic fixtures. Once you've gotten rid of a ring, weekly cleanings should keep it from coming back.