Pool chemicals do not expire, although they become less effective if stored for long periods, according to Omni Pool Equipment. Some pool chemicals and test strips include a use-by date to indicate when the product is most effective.
The reagents used to test pool water also become less effective with time. Reagents should be replaced if the bottle is stained or if it contains particles or a crust on the top, according to Taylor Technologies. Storing reagents in a refrigerator during the off-season may extend the liquid's shelf life. Pool chemicals should be stored in a cool, dry area with good ventilation.