In general, I expect that 4 years is not too old for an alkalinity test if the fluids have been tightly sealed, because there is not much that can really go wrong. Since you got an unexpected answer, however, I'd confirm it with a new kit before acting on it.
FWIW, the owner of Salifert (Habib Sekha) frequents this forum and will likely give you a clearer answer on expiration dates.
__________________
Randy Holmes-Farley
|