I am getting a tingling sensation around my ankles. What is causing this?

There is probably too much salt in your foot bath water. If you have a tingling sensation around your ankles when you turn on the machine, you need to turn off the unit, remove some of the water, and replace it with fresh (warm/hot) water to reduce the salinity of the water. If you do not see any bubbling action around the array after approximately 10 seconds, add a dash or two of salt, not more than 1/4-1/2 teaspoon of salt.
Some people are more sensitive to the current in the water than others. If you are one of these lucky ones, shake in salt a little bit at a time until there is some fizzing at the array. You can always add more salt throughout your session as needed.

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