My fiberglass bathtub has a nonskid bottom that is terribly difficult to get clean. I have found that the best thing is to scrub it with baking soda. It also seems to stay clean for a long time after I do this. For a little added cleaning power, after it is all scrubbed, I add and scrub a little dash of vinegar all around, scrubbing quickly as the fizzing action only lasts a few seconds. The tub is just gleaming when I get done. It is an amazing cleaner for fiberglass.
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