HTH Sock It Pool Shock-N-Swim - 18 x 1-lb. bags
HTH Sock It contains 45% available chlorine making it a very powerful yet safe chlorine shock treatment, swim immediately after use!  Controls algae, bacteria and other organic contaminants.  Use HTH shock on a weekly basis to prevent algae growth.  Dosage = 1 to 2 pounds per 11,500 gallons.  Calcium Hypochlorite.