The HTH Shock Treatment is the perfect solution for keeping your swimming pool water clear and ready for fun all season long. It increases the chlorine level in swimming pools to kill bacteria and algae, and is effective for all pool types including pools with liners and Gunite pools, and saltwater pool systems. Simply apply directly to pool water as needed and test pool water and shock weekly to keep free available chlorine levels between 1 and 4ppm. This shock treatment kills and prevents bacteria and algae, keeping water clear with visible results in just 24 hours. One bag treats 13,500 gallons and won't fade vinyl pool liners. The package includes 15 1-lb bags of shock treatment and 15 test strips for your swimming pool. Keep your pool crystal clear and healthy with HTH.