shelf life on chemi-pure: 2, 5, 10 yrs??

[nemo g]

just curious if someone knows the shelf life for boyd's chemi pure.

a bud of mine picked some up for pennis from a closing lfs. hell give me some, but before we use it id like to make sure its viable.

whats the worst that can happen?

will it foul the water, or just not work?

thanks