check for the expiration date, for the life of me i can't remember what it is, but i think that there is a list of numbers on the box and the last four should be the expiration date. chances are, if you've had it for four years it could very well be expired. i would go ahead and use them to see what kind of readings you get.
for the second
nitrate bottle, make sure that you bang it against a counter or table a few times, and shake it for two solid minutes, maybe more since it's been a while. the ingredients crystallize and you'll get a false zero if they aren't mixed properly
oh, and this is assuming that you meant an
API freshwater master
test kit