Unless things have changed in the last 25 years or so the ammonia test
kits that use nestlers reagent are supposedly only good for a limited
time.. the ROT 'was' 1 year so that is how often I replace mine..
(Since I invariably loose, misplace, spill or contaminate one or more
of the parts to the kit it is easy to remember to replace...)

1 year is still what is recommended by the KHA instructors. The test
manufacturers claim they're good for 2 years. Course conditions like
freezing & over heating can degrade all of the above. ~ jan

~Power to the Porg, Flow On!~