Actually, you can use the SWCG for routine chlorination, but not for 'shocking', for spring start-up, for winterization, for algae, etc. In other words, when the pool is fully 'adjusted', use the SWCG. When you are having any sort of problem with the pool (algae?), or when the chlorine needs a boost (party?), use bleach if your CYA is OK, or dichlor if it's low.