Shelf life for Hypo Clearing Agent?

Greetings, B&W Dinosaurs;

Last night, developing some Ilford HP5 rolls, I mixed some new working
solution of Hypo Clearing Agent. The stock solution--stored in a cool, dark
darkroom--had been mixed about a year ago, and smelled VERY strongly of
ammonia. How come? Any ideas on the recommended shelf life of this stuff?

Yes, I mixed a fresh batch, but can anyone explain the strong odor? What
are the decomposition products of clearing agent? Rich Knoppow?

BTW, it is GREAT to see so many diehards still fussing with black and white.
SILVER HALIDES FOREVER!!

Dick Behan
Lopez Island, WA