New long-lasting advanced, concentrated formula repels rust and iron stains in toilet tanks and bowls. Cleans with every flush. Easy-to-use, just drop in tank and forget it. Rinses away rust stains with no scrubbing. Keeps toilet tank/bowl stain-free. Each tablet lasts up to 30 days. 2 tablets per box. Safe for plumbing and septic tanks. contains no phosphates. Do not mix with bleach or any other household cleaner. Do not use with other in-tank cleaners.