Pool store has a good deal on 12.5% "bleach", 10.99 for 4 gallons. I would like to stock up but do not know how long it will keep before it is say 10%. Apparently they usually only stock 10% but couldn't get it so got 12.5% and are selling it for the same price. They only have a few cases left and I already bought 4 cases. I will be storing it in a cool dark enviroment. What do you think?