A friend of mine, who's a big boater, told me about this stuff called X-14 - it's a mildew remover. It's not easy to find, but you can get it on the internet. I was having a real problem with mold on my fiberglass, tried many products. Then I heard about the X-14. You spray this stuff on, wait a few minutes, and rinse it off. I tried it, and I was truly impressed. My boat hasn't looked that good since I got it. It does have bleach in it, plus other stuff, but it is not caustic like some heavy duty boat cleaners. It's made by the WD-40 Company.