After reviewing the scientific literature, it was found that many researchers concluded that: the more concentrated the solution, the more effective it is. Based on this observation, KATHAROS worked for more than a year to produce the most concentrated colloidal silver solution possible via electrolysis: their tests, allowed them to consistently achieve a concentration of 40 PPM.

The claim that solutions over 10, 15 or 20 PPM are less effective has been flying around for a while. There is no scientific data to back up this theory.
More information can be found here.