The table at the bottom of this link gives the half-life for bleach or chlorinating liquid at various concentrations and temperatures. This is for high quality product without even trace metals in it. So bleach at 6% or 8.25% if kept at cooler room temperature will last for months. 12.5% or higher chlorinating liquid won't last as long, but again if prevented from getting too hot it should still not degrade too much in a month or two. I use 12.5% chlorinating liquid and I buy one month's worth at a time and never noticed any significant decline between the first and last dosing in terms of expected FC rise.