Beck would recommend to use a low frequency. Beck used 3.92 Hz so 4 Hz would be the Beck frequency. At the low frequencies, some people absorb druqs and other substances at levels up to 20 times the normal amount. The higher frequencies are suppose to stop this from happening.
For the purest silver and smallest particle size. Use the lower 1 mA setting with distilled water 3 ppm contamination or less.