One other thing to consider if you are looking at "pool store liquid chorine", if it is sold in carboys that are filled on premise then it is being delivered to the store via tanker and stored in large tanks on site (I used to work in such a store and I can tell you that there is no greater joy than refilling carboys in the middle of summer in the hot Florida sun!). One time when reordering the bulk chlorine from our supplier I asked then if it was actually stronger than 12.5% (since I had notices that FC were a bit higher then expected in some customer's pools) and they said it was closer to 17% when it left their facility to compensate for the loss of strength on storage that the 12.5% was a minimum of what the product would be.