To make colloidal copper with low voltage electricity in distilled water, I added some salt. However, the added salt shows up in my PPM counter device, before I turn on the voltage to copper rods.

How can I discount salt PPM after the process completion? The catch 22 is to make this process work salt is needed, yet the added salt distorts the actual PPM of the colloidal copper that is made. Is there a way to know PPM of copper colloidal?