This Pool Block PB-80 is a natural pumice stone tile and concrete algae rust lime cleaner that is perfect for keeping your in-ground pool clean and healthy. The product is made by UNITED STATES PUMICE COMPANY and is a great addition to any pool equipment and parts collection. With its unique formula, this pool block is perfect for removing stubborn algae and rust stains from your pool without damaging the surface. It is ideal for use on concrete, tile, and other pool surfaces. This product is a must-have for any pool owner who wants to keep their pool clean and inviting for swimming.