As an experiment, take a store bought water bottle and test the water in it. If it gives a weird result there is a good chance your test kit may be messed up or expired.
Here is how to check the bottle to see if it is expired.
Each reagent bottle has a Lot # printed
on the bottle. The last four digits are the month and year of
manufacture. Example: Lot # 28A0102. This is a pH reagent manufactured
in January of 2002. Pond Care Wide Range pH, ammonia, High Range pH,
Nitrate, phosphate, Copper, calcium and GH all last for three years.
nitrite and KH will last for four years. Freshwater pH(low range) and
Pond Care Salt Level will last for five years. I would not trust these
kits after they have expired.
Info was found on
http://www.fishlore.com/fishforum/te...kit-users.html