he said the bathtub, not a foot bath. i use an ionic toothbrush, have for 15 yrs. plaque is positive, so it emits negative ions to repell plaque. what does a bathtub have to do with an ionic foot bath? and, if you are trying to get heavy metals out of your brain, lymphatic system and organs, an ionic footbath will not work. you have to chelate with supplements or drugs to do that.