i was told it does go off, but i have had mine in the original bag tightly sealed and it is still ok, i would say because it has condensation in it , it has taken some of the goodness out of the resin, i might be wrong, i have to change my resin every fill up in my ibc tank, but water round here is well hard, 499 out of the tap, but still manage to get it down to 000.
Haydn