Question For No3 Dose

I try to figure how much consumption of NO3 I have in my tank. I add NO3 from the dose of KNO3 and from my wc water.
These are the only sources or I also have more amount from my tank, like nitrogen cycle fishes and plants??

 

in general I try the EI method with 50% wc once per week. I dose 7.5 from KNO3 and 7.5 from my water change. So I add 15 ppm weekly. If I have 2 ppm consumption per day, my plants take 15 ppm per week. So is it logical the 10 ppm of NO3 I found at the end of the week by test, to be the rest from nitrogen cycle??