HTH, 37.5 LB, Super 3" Chlorinating Tablets, Sanitizes Pool Water, Stabilized, Sun Protected, For Extended Chlorine Life, For Use In Simmer Or Floater, Protects Against Bacteria & Algae Growth. Active Ingredients: Trichlors-S-Trazinetrione 93.6%, Zinc Sulfate Monohydrate 3.5%, Other Ingredients 2.9%, Available Chlorine 84%.