Pro Guard 1" Tablets Reduce The Growth Of Harmful Algae And Micro-Organisms In Pools. Tablets Are Not Only Slow-Dissolving With No Clouding In Water, But Also Uv-Stabilized To Reduce Loss Of Chlorine Residual Due To Sunlight. They'Re Sized To Fit Or Refill Most Popular Residential And Commercial Chlorinators And Floaters. The Active Ingredient Is Trichloro-S-Triazinetrione, With 90-Percent Available Chlorine. Each 1" Tablet Weights 3Oz.