Ionic Foot Baths--Negative and Positive Charges

Erchonia makes a foot bath with both negative and positive charges.
What are the different purposes of each? My understanding is that
negative is alkaline and adds electrons, that is generally what is
needed. What is the point of positive, unless the person is too
alkaline, which is suppose to be rarer. I tried the erchonia foot
bath, felt nothing with the negative charge and then got a headache
with the positive charge so i stopped it early. The water started
changing color a little with the positive charge, it got a little
olive like, but most if not all of the color and flecks seem to be
from the copper array/instrument of the machine. Any thoughts?

Paul