Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
So, if the baseline reading for NO3 was never more than 10 ppm before dosing, then you can reasonably assume that dosing has caused the majority of the increase. Calibrate the test kit, but in the mean time, yes, stop dosing the KNO3.
If the plants need more K then use K2SO4 or other source of K.
You may find that the plants are capable of removing all the NO3 down to 0 ppm. Before you were dosing anything it is possible that they were short of something, and this limited their intake of nitrogen. Now, with any possible deficiency addressed, they will be able to remove more N from the tank. Monitor this, and begin dosing KNO3 as needed.