Thanks, Watermom. I'm taking a sample to be tested today. I've been reading the Pool Forum for a few years and have spent the past few weeks reading posts related to minerals in the water. The Blue Shield Sani Shock 2 Super Shock Treatment (1 lb. bag) contains: calcium hypochlorite - 47.6%, other ingredients (not listed) - 52.4%, minimum available chlorine - 45%.