I am a HUGE fan of cleanliness. The dark smudges on my tub that won't come off drive me crazy and that is why there is constantly a scrubber on the ledge of our tub. I can hook the scrubber to my foot and scrub while I am showering but it is impossible to get rid of the black smudginess. If I scrub too hard the tub starts to flake because parts of the bottom are peeling and soon I have a bunch of tub flakes all over and it is just sooo frustrating. Any ideas on a good product that I can let sit for a bit then just scrub a little bit to get the black to go away???