We just bought a fairly new house with one of those big Roman tubs with a non-slip surface. The tub is fiberglass. The owner remarked that they had never been able to get the bottom of the tub clean after it got dirty.

I read many messages on this forum this morning and was all ready to try the baking soda/vinegar/ etc solutions but decided to try the MagicEraser first because it required no mixing. Voila! In about five minutes and with minimal effort, the tub looks like new. There is only one nickle-sized spot that still needs further work. My husband and I were amazed.

I plan to put the Fiberglass Gloss on it now to seal it against future dirt (which shouldn't happen because I hate these tubs anyway!).