This powerful cleaner quickly removes most stains from gelcoat.This powerful, acid-based cleaner is a proven way to deep clean and remove a wide variety of stains from gelcoat. Typical uses include removal of waterline rust and scum stains. Do not use on aluminum surfaces.Key featuresRemoves rust stains and waterline scumBrush-on/rinse-off, biodegradable formulaWill not harm fiberglass, gelcoatsWorks instantly to remove the toughest waterline stains