Sanco has several different forms of bacteria, liquid and dry. 

Our liquid Natural Pond Cleaner can last for more than 5 years if kept in a stable temperature unopened.  Once opened you should use Natural Pond Cleaner within 2 years.  Once opened and stored you may loose some spores over time. 

Sanco's dry packs and spikes can last at full strengh up to 3-4 years.  Spores may fade over time, but some germination could be expected indefinietly.