Here are some of PoolDoc's answers from PoolSolutions.com:
http://www.poolsolutions.com/tips/tip09.html
http://www.poolsolutions.com/tips/tip70.html
Notice that there is a small, but real danger to chlorine. However, the danger from NO chlorine is far, far greater. 180 cancer patients in Peru were prevented by removing chlorine from drinking water--but 4,000 deaths from water-borne diseases were created!
Notice also that chlorine is chlorine. Pool stores sell bleach every single day, packaged as "Liquid chlorine" or "Liquid Shock". The first is 6% Sodium Hypochorite--same as ultra bleach. The latter is 10% of 12.5% Sodium Hypochlorite--about twice as strong, but the same stuff again. They just don't want you buying bleach from the grocery store or CostCo instead of buying your chlorination chem from them. If they don't sell 100 $100 buckets of chlorine because those 100 buyers have switched to bleach, they've lost $10,000 in gross revenue.
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