I work at a natural health clinic, and the flecks and discoloration are simply a reaction of the water with your sweat causing a chemical reaction with the metal (zinc) rings on the unit. Some of the newer units (not as popular) do the detox foot bath without the disgusting residue from the zinc rings decomposing. Look for a practitioner with an ionic foot cleansing unit or a newer befe. The color is just a selling point to help make you more psychologically hooked on the footbaths, wanting to come in more and more. Another thing practitioners like to do is to over-emphasize the "smell" after the footbath to help you feel like you had a really good cleansing session. I do not doubt that they are helpful, and believe that they are very therapeutic. But please don't let these natural health care practitioners let you think you are getting more from the footbath than you really are. I have to clean sinks after the footbaths, and the colors on the zinc ring perfectly match the stains on the sink, and spraying/disinfecting the unit causes flakes (browns/blacks) to fall off. The color and amount of sediment is due to the amount of salt (or other chemical) put in the water, and how many footbaths the rings have been through along with the electricity being pumped into the water.

happy health.