When I set up my current diminutive darkroom. One of my rules was to never mix chems in larger than 1 liter volumes. Of course I am too cheap to pay premium prices for the smaller packages so I buy Gallon packs and split them into quarts. I was amazed by how quickly and dramatically the Dektol discolored in a zip lock bag. Then I tried one of those vac 'n' seal machines which was better but surprizingly, the Dektolstill discolored in fairly short order. Now I use the vac 'n' seal and then put the individual packets into a zip lock bak and roll out the air. This seems to fit my needs although maybe I'll try storing in the freezer as was mentioned.
My only point here is that Dektol is quite hard (but not impossible) to keep White once out of it's original packaging