Just picked up a used pontoon boat that has black stains on the side of it(not the pontoons but the side walls) from what looks like while the boat was covered, the rain ran off the cover and stained the side of the boat. Any idea how to remove these stains? I have tried the following with very little results.
1. Muriatic acid
2. Zing (Pontoon aluminum cleaner)
3. Various stain removers
1. Muriatic acid
2. Zing (Pontoon aluminum cleaner)
3. Various stain removers