Need advice on really long fishless cycle. The problem - lack of nitrates

Hello Everyone:
Need advice on really long fishless cycle. The problem - lack of nitrates.

Have 20 gallon tank, started fishless cycle 7 weeks ago.I'm adding Ammonium Chloride as a NH3 source.
Nitrites started to appear at in a week after starting cycle but no  nitrates. I've increased temperature from 78 to 86 degrees 2 weeks ago. Today I did 5 gallon water change, I have few plants in the tank.
Conditions: Temp 86 degrees, GH 4 degrees, KH 2-3 degrees, Ph in range of 7-8 (both Ph and KH are monitored, alcaline buffer added if needed).  Have Fluval C3 Power Filter with water intake extended to the opposite corner of the tank, this ensures good water circulation. Withing the first week I was adding SeahChem Stability, also adding Stability once in one-two weeks.
Dynamics: Adding 25 drops of Ammonium Chloride every 12 hours, this amount target Ammonium concentrations around 2.5 ppm.
In 12 hours Ammonium is 0 ppm, NO2 is 0.25 ppm, NO3 is 0 ppm.

I guess everything is set up in good order. Please advise on completing the fishless cycling - converting NO2 to NO3