Old Spray (3+ Months)
When the sprayer bottle is properly protected from light, and kept in a cool place, the mixed STS can remain viable for months.
New Batch Every Business Day
We at silverthiosulfate.ca make a new batch every day we ship. We NEVER use old materials, and we always print a mixed on date on every bottle.
Simple Visual Inspection
You can check to see if the solution is still viable by pouring a bit out in a clear glass. The solution should be crystal clear.