I've been getting my 26 foot 1985 Carver Santa Cruz ready for sale, I made the mistake of parking it under birch trees for two years.
I knew it'd get covered in birch tree snot, but I figured it'd just power wash off easy enough, which it did - even if it was a lot more work than I expected.
What it left behind though were brown stains deep into the fiberglass and paint, the entire boat was polka-dotted with dime sized splotches everywhere, I tried starbrite hull cleaner - the one with oxalic acid in it and the stains barely budged. Tried a couple of other products also but they were a pain in the butt (the gel) and/or expensive.
On a whim I noticed I had a bottle of Tilex mold and mildew remover and I sprayed a test patch.
It was incredible! In about 2 mins the stains just faded away to nothing with no scrubbing at all! I used up 4/5ths of a bottle and the entire boat is the cleanest its been in 8 years. The only stain it didnt remove was a rust stain.
It also stripped away all the wax and now I have a semi-gloss finish but thats not a big deal since it needed to be waxed anyway.
It just blows me away that Tilex works better than products 4 to 6 times as expensive and was a lot easier to use.
Just thought I'd pass it on.