Be sure to wash your hands before performing the test. Bromine, chlorine, or other chemical residues on your hands can skew the test results. Check the expiration date on your bottle. Test strips have a definite shelf life. Beyond that date, you cannot be assured of accurate results.
False readings mean bad tests, wasted chemicals, or equipment damage.
Replace expired strips. Dip the strip to completely cover all the test pads, but not too long in the water. Excessive time will invalidate the test. Also keep in mind that in instances where the amount of bromine or chlorine in the water is quite excessive, it can actually start to bleach-out your readings over time. You will have to wait until the bromine or chlorine level comes down to get an accurate test result.