HTH™ Shock is the original swimming pool shock designed to boost chlorine levels and kill bacteria and algae for a clean, clear pool. Traditional chlorine products contain cyanuric acid (CYA). When too much CYA builds up, it can cause overstabilization or chlorine lock and cloud your water. The fast-acting, fast-dissolving Cal Hypo based formula in HTH™ Shock provides chlorination without adding extra CYA for a beautiful sparkle all season. This pool shock is great for all pool types and won't fade your pool liner.Follow the on-pack instructions according to your pool size to add HTH™ Shock directly to swimming pool water or skimmer. For best results, apply HTH™ Shock as part of your weekly pool care routine to keep free available chlorine levels between 1 and 4 ppm.