Lloyds Laboratories 39600 Captain Phab Fast Hull Cleaner, 1 L bottle (32 oz)

Brush or spray on, allow 5 to 10 minutes in ambient temperature, then rinse it off. For use on fiberglass only. Easy to use and works instantly. This is a buffered acid cleaner. Formulated to ease End-of-the-Season haul out cleaning. Removes waterline stains, algae stains, rust and gas exhaust stains. Excellent for Great Lake applications and barnacles.