salifer test kit?

[africangrey]

Dr Randy,
Do you know if Salifer kit or test kit in general have expiration date, the last time I test my water was about 4 years ago to monitor the performance of Ca reactor. But today I used the same old kit that have been collecting dust to test the water the KH was way low 3 dKH. What should I do to further validate the result or should I just get a new kit instead, I mean do they ever go bad after a certain period of time. Thanks.
-A