I connected the graters (1" apart)to the center of a long piece of wood that fit across the middle of the plastic container. I did this to be able to safely put my feet on the outside of the graters. I did fix it so I could change chairs to have different polarities and boy! Did it make a difference. I had so much black scum floating in the water and on top and also dark red. The footbath water is now settling so I can see more concentrated debree. I tried to look at what was on the graters but I couldn't tell what I was seeing. Sure wish I had a microscope, not that I would know for sure what I was seeing. Thank you Ladylove for all the information you have contributed, especially about changing polarities and having the graters between your feet.
Tomorrow I will go get pure stainess steel rods and test them in the bath water. I may connect the graters or steel rods to a longer piece of wood to go lengthwise in the plastic container and try to turn my feet sideways and see if I can see anything coming from my feet in the water.