HTH, 13.3 Oz, Shock Treatment, Minimum Available Chlorine 45%, Kills Bacteria & Organic Contaminants, Active Ingredient: Calcium Hypochlorite 40-55%, Cal Hypo. HTH® shock treatment, 13.3 oz. is an effective, multi-purpose product that sanitizes, clarifies, helps prevent algae and shock treats your pool. It is convenient, easy to use, and won't over-stabilize your pool.