I base this upon the manufacturers recommendation of storage temperature of 60F to 86F. Air temperatures in the shade in summer here can push 100F and I've recorded temperatures in my storage box on my truck at better than 140F. It was hotter still in the cab.

I e-mailed Potable Aqua a long time ago asking for guidance for shelf-life at temperatures outside the recommended range but they never got back to me. So, for now, and until I get more information, I figure chlorine dioxide based treatments are only reliable for six months under local conditions. Given that decomposition for temperature are often exponential curves and given the summertime temperatures in Florida and the SW, six months might be optimistic.

Of course in those location where 86F is a hot summer day this is less likely to be an issue.