Does anyone know how to tell how old a pool chemical in the test kit is? They have lot dates, but I don't see any actual dates stamped on them. I think one of the test kits I purchased this year, New from the pool supply store, is actually old. When I purchased the TF-100 and used the K-1000 Taylor kit chemicals they seemed more accurate. I got a higher chlorine count than the other kit and I tested a couple of times.