I think you are absolutely right to be concerned about electrolyte deficiency if you do any high colonics. Really one doesn't know what in the heck they flush away that might be beneficial as Science is always discovering something new.
You might want to research Stone Free for both kidneys and gallstones. I personally have found it helpful, though after months of using it I still got out stones with a liver flush. The thing is most, not all, of the stones were very tiny. It seems Stone Free shrinks them. A Liver Flush also revealed chaf which I do not think Stone Free helps to remove. But, it is a product that can be useful in some ways.