It has been frequently reported on this forum that the 12% stuff was unstable and I had a discussion with the manager of a local pool store manager and he readily admitted the degredation is a problem. He has 2 small ( 5000 litre ) tanks and gets weekly small deliveries so he can control his stock on a first-in first-out basic. Keeps it fresher than one 10,000 gallon tank where new stuff gets mixed with old stuff.

There is a chemical engineer type here who worked at a chlorine production facility and posted recently. I hope he sees this thread and can cite some more authoritative sources.