Doheny"s Super Shock chlorine shock for your swimming pool is fast-acting and features calcium-hypochlorite as the active ingredient to help clear the most contaminated pools. A 2-3 year shelf life for each bag makes this a convenient value. Dosage: 1 lb. per 10,000 gallons to provide dosage of 7.5 ppm free available chlorine. Instructions for use: Dilute shock in bucket of water. With pump running, broadcast evenly at deep end. Use brush to disperse any particles that have settled to bottom. Let pump run for 6-8 hours minimum after applying. We recommend applying shock at night and letting pump run overnight. Do not re-enter pool until chlorine is 1-4 ppm.