I just started dosing nitrates yesterday. Hopefully I can see some improvements. Do you mind telling us what your mixture is and how much do you dose?
I use this calculator recommended by Randy Holmes Farley along with the adjustment factor for sodium nitrate:
Here's one. You can enter potassium versions and the answer will very close (closer than you can detect with a hobby kit).
For example, pick the entry for potassium nitrate, and if you want high accuracy when dosing sodium nitrate, multiply the answer by 0.84 to get the dose needed (so 0.84 grams instead of 1.0 grams).