If you're following the sticky, and you have low light, there's no way you don't have measurable amounts of nitrates. First make sure that the test kit isn't more than a couple years old. The batch number is the month and year of manufacture, and if it's the API test kit, it's printed at the top of the bottle.
Then read the instructions a couple more times. The nitrate test is surprisingly complicated. It's really important to shake the heck out of the bottle before mixing, and then shake the heck out of the tube after mixing.
If you're following the EI sticky, you're adding something like 1/2 tsp 3x per week. Is that correct?