ZEP Shower, Tub & Tile Cleaner
$1.98/The Home Depot
Features: Touted as safe for fiberglass, this product caused our gelcoat no ill effects over time. Its acidic base foams on a soiled surface, indicating the stain-removing reaction.
Instructions: Apply directly to the wetted nonskid surface, let stand and rinse.
Performance Report: It failed on the multiple-stain test. Only bleach removed the wine stain after this cleaner turned it dark gray. It substantially removed the cola stain. Fish guts were easily brushed away after application.