I use 12.5% chlorinating liquid and it most definitely smells like very strong bleach. Though the higher concentration of chlorine does break down faster, if it is properly stored in shade and away from high heat it should last at least a month or so. The half-life of 10% chlorine at 77F is 220 days (that means it loses half its strength in about 7 months), but if it's exposed to high heat or was left out in the sun, then it will break down much, much faster.

Richard