Lol, well I can't be sure it's reading nitrites at all. I'm just guessing because I tested it before and the water in the test tube turned distinctly blue. Then I tested it again today and it was a darker blue and the next color on the chart is purple. So I'm guessing it's detecting something but not enough to change it to purple.
Mine did that. I remember it appearing in between, never quite either of the steps, but not progressing after a few days testing, either. I just left it for a while (I don't remember how long) and the next time I tested it turned purple so quickly I was like .