Hi jw, welcome to reefs.org. Generally, yes, there is an expiration. On quality kits it's going to be stamped, usually on the reagents themselves. Hopefully you've at least got a lot number, and you can contact the manufacturer to learn the age of these tests.
I'll suggest you be careful about using questionable tests, of course (not as though you didn't realize this, but these threads are read by many others as well), there is not only a great variability between different manufacturers, but storage conditions and age can all be factors that affect the reliability of said test.
Best of luck!
