API test kit - vials changed overnight?

[Moogled]

Hey folks, I'm out of town but was told by my GF that the tank water tests she performed for NH3, NO2, and NO3 were 0ppm last night.

However, she noticed that the same vials now show higher. I understand that the instructions indicate that you add the appropriate # of drops, shake it and then wait 5 minutes.

I've never had them change colours even after two days so it was strange that it happened for my GF.

Has this happened to anyone before?

Is it an indication of a faulty test kit?