the contents can oxidise, like beta carotene can reduce over storage time, and other antioxidants. But really it depends on how you store it: amber glass first, clear glass second, plastic tub third, plastic bag last. Reduce light, heat (some debate on this as spirulina is said to withstand quite a lot of heat) and air entry. Then storing large quantites should be fine, and it will save you a heck of a lot of money!
When others asked the truth of me, I was convinced it was not the truth they wanted, but an illusion they could bear to live with. Anais Nin