I just got a new API test kit for xmas, replacing a very old one I have. I believe the old one is 7 years old, although the ammonia test kit is somewhat newer, but still probably 5 years old (I did a lot of ammonia testing the first couple of years).
One difference with the new kit is all the bottles are stamped with an expiration date about 5 years from now. None of the bottles in the old kit have expiration dates.
Here are the results:
- ph Low 6.4: Both kits tested the same
- ph High 8.2: Both kits tested the same
- Ammonia 0.0: Both kits tested the same
- Ammonia 2.0: Both kits tested the same
- Ammonia 4.0: Both kits tested the same
- Nitrate 0: Both kits tested the same
- Nitrate ~20ppm: The older kit was a noticeable shade lower, maybe making it low by about 5-10ppm.
- Nitrate 45ppm: Both kits tested the same, but it's very hard to tell the difference of even 20ppm at this level.
- Nitrite 0: Both kits tested the same
- Nitrite .50: Old kit .25, new kit .50.
- Nitrite (very very high): Old kit .50. New kit through the roof.
For the Nitrite measurement, Iím used water from a tank that Iím currently cycling. The old test kit has been consistently measuring .5ppm the past week (which seems too low and too consistent). The new kit shows it through the roof, which seems right. Also, the old kit changed colors right away, and has a ďdirtyĒ look to it.
For the .25 Nitrite measurement, I used RO water with 1 drop of the water from the cycling aquarium, which is about 1% of the water measured. So that probably means the tank is at 25ppm, which is believable considering it was done with ammonia cycling a week ago, and I havenít done a water change yet.
My conclusion: don't throw out your old test kits, but don't count on the nitrite kit being accurate, especially for high nitrite values.