The expiry date (lot number) for API is printed on the bottle itself. Unfortunately there is really no way to check the lot number on the kits until the kit is purchased. As such I have wrote a email to API and here was the reply,
The expiration of the reagents will vary, each reagent bottle has a Lot # printed on the top front of the bottle. The last four digits are the month and year of manufacture. Example: Lot # 28A0110. This is a pH reagent manufactured in January of 2010. PondCare Wide Range pH, Phosphate, Copper, Calcium and GH all last for three years. Ammonia, PondCare Ammonia, Nitrite, PondCare Nitrite, Nitrate, High Range pH, KH, Freshwater pH(low range) and PondCare Salt Level will last for five years.