Shock treat your pool at least once a week to kill unwanted bacteria and algae. Shocking gives your pool the boost of chlorine it needs to keep the water clean and clear. The hth Benefit: This is an effective, multi-purpose product that sanitizes, clarifies, helps prevent algae and shock treats your pool. It is convenient, easy to use and contains no cyanuric acid (CYA), which means NO RISK OF OVERSTABILIZATION.