One other reason to use bleach as opposed to the other types of chlorine is the byproducts. Show her the chemical name for trichlor or dichlor. The other stuff going in beside the chlorine is not good to be putting in the pool continually - a buildup of cyuranic acid can cause chlorine to not kill the bacteria and viruses at the same concentration of chlorine. The only other reaonable chlorine sanitizer is calcium hypochlorite. The byproduct makes the water harder. The water doesn't feel as good, and can cause staining and buidups at the water line and in the plumbing of heaters. Bleach byproduct is simnply salt - This makes the water softer (although not by much at the levels used for sanitation).