Azoo No3 Test changes over time

[pehcao]

Hello guys,

I've been using the Azoo No3 test lately following the instructions in the box resulting in very low No3 tests almost every time on my planted 20gal aquarium. However, I've noticed that if I leave the tested water lying around in the test tube for long periods of time (hours), it changes color to a much deeper purple indicating a whole other range of results.

What should I do in this case? Should I listen to the immediate result, or to the later result?

[xXInkedPhoenixX]

As a general rule- tests- when done correctly from instructions and -checked/read when instructions say the test is done is the time the test should be most accurate. After that generally chemical reactions are still happening and will change color. This happens with test strips and can happen with liquid tests IME.