Funny, I had the opportunity to talk to the son of the owner of the company we buy our shock from last year. He said that 'in the box' (ie protected from UV) it was at full strength for 90 days, and after that it degraded "slowly". I do not know about regular bleach, sold in the stores (I made sure that all the shock was taken back at the end of last season - who knows what they do with it, test it and resell it as 6% bleach?) . As a simple and easy test, look at it if it is very yellow/green, it's probably good - if it looks like water, it probably is (just water). Many liquid products are affected by UV, when I worked at a package (liquor- for the folks not in the NE) store, I learned that beer spoils with UV exposure, therefore beer in brown or green bottles will last longer. ( What's the use of having a beautiful pool without a case of cold beer to drink? )
Hope this is helpful, if not, rag on me mercilessly