I sometimes have liquid chlorine, the pool store stuff in carboys, left over at the end of a season. I store it in the garage over winter and then use it after the pool has thawed, just to dump in a dose to make life tough for what algae might want to get going. At this point it really doesn't matter what the strength is anymore because I'm not yet testing or balancing. Whenever I buy a refill I do test the concentration of it. It's sold as 14% but my testing usually puts it at 11%. Good info to have.