What really cleans the yellowish/grayish streaky ring around the tub from constant shower use? I've tried a couple of different spray on cleaners and the ring is still there. I presume it's from soap scum (98% shower use only on fiberglass tub surround and soft water). I'm tired of wasting money on products that simply don't get rid of it. What have you all found that really wipes the ring away (and without having to keep cleaning the tub weekly--who wants to clean their tub more than once every few months. Not me.). Thanks