By Patricia Fitzgerald
Misinformation about the useful life of reagents is widespread. I’ve lumped several myths together here that can all be cleared up with the simple understanding that reagents are by nature perishable, just like milk, produce or medicines.
This is true whether they are liquids, powders, crystals, tablets or test strips, although shelf life does vary by type. For instance, if kept dry, powders and crystals are very stable; acids are also long lived. Other reagents are more susceptible to degradation, like DPD or silver nitrate (AgNO3) reagents. (Their opaque bottle is your hint the reagent is very light sensitive.)
Date of manufacture is not the controlling factor when it comes to shelf life—storage conditions are more important. When not in use, reagents do best in a cool, dark place, away from volatile treatment chemicals, especially chlorine and bromine. Inventory should be dated and rotated according to the first in, first out (FIFO) principle.
Ideal storage temperatures are between 2 to 29 C (36 to 85 F). If you must choose between a hot warehouse (or vehicle trunk) and the refrigerator, opt for the latter for longer-term storage.
Read the full article: Busting Water Maintenance Myths