It is normal for at least one of the electrodes to become discolored after just a couple of uses. Typically, the black electrode (the negative side) gets discolored faster or more. The discoloration does NOT affect efficacy. What DOES affect efficacy is calcium or mineral deposits that accumulate over time due to water hardness. Every 3-6 months (depending on water hardness), the electrodes should be soaked in a half water/half vinegar solution overnight and then scrubbed and rinsed to prevent loss of efficacy. We often get calls or emails from customers about a year after purchase that their device is not as effective. A good cleaning always does the job.