When I started dosing by hand I used some store bought alk/calcium that I had from before I left the hobby long ago. So I was using some that was a half full gallon that had been in my garage for over 10 years.Once baked how long can it be stored for?
Like @homer1475 stated Randy had said that it can basically be stored indefinitely. If you mean as a powder after baking it I don't have a clue, but my guess would be not very long before it would need to be baked again before use.