Red Sea Test kit problem - Nitrates

During my cycle, the test was working fine, showing a pinkish color at about 5ppm. Once my cycle was complete and i started stocking the tank, it turned bluish, 0ppm.

However, the last 3 tests i have done with it, the water is just clear. It starts off bluish, but by the end of the 9 mins, it is just clear. Kinda hard to do a reading with clear water. Does anyone else have this issue, or know why?? Thanks
 
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