Mary Kate on/off always works great for me, never had the need to search for a different product.

To get the stains off this stuff is the best.Fountain of Youth Products, Power One. Spray it on with a garden sprayer and hose it off that is all you need to do!! The boat still feels like it has just been waxed after it is hosed off!!

Muriatic Acid. commonly used to clean concrete and swimming pools....about $5-7 per gallon at a pool supply store......will INSTANTLY remove rust stains from Gel Coat....you can even dilute it 50% with water.......spray or brush on......hose off. Mary Kate ON/OFF is good stuff...but about $50 per gallon!!!!! Don't get either on a GALVINIZED metal (Trailer)....eats the galvy right up!!!

Interesting. Gawd I hate working with that acid on my pool gunnite, I always manage to get a whiff

I also use Power 1 - just put it in a sprayer, spray on and rinse off with water. No rubbing. It works great on yellowing I get at LOTO, but not as well for some friends on local ponds in central IL, who do better with acid based products. I also buy it directly from Fountain of Youth by the case of gallons (4). Runs about $30 a gallon including shipping. I like it because it is not acid based, so I don't need to worry about it getting on the galvanized lift. I usually let it sit for about 10 minutes before I hose it off.

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I had some rust on siding from a faucet that is fed directly from the well, this took years to build up. I did have to do some scrubbing with the Power 1, but it only took about 15-20 minutes, before and after pics.