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Why are my ORP (Oxidation-Reduction Potential) measurements nonsensical?

Ozone is a very powerful oxidant and can elevate ORP (oxidation-reduction potential) values to unsafe levels. Residual ozone and oxidation by-products such as the oxyhalides can produce elevated ORP readings.

However, ORP measurements are notoriously misleading and often incorrect. Drain and refill electrodes with the correct filling solution and verify their operation with the following simple procedure:

Dilute an ordinary two ounce bottle of Tincture of Iodine (USP Grade) to 16 ounces (473 mL) with deionized water. After mixing, the fresh solution should measure between +440 and +455 mV. If it does not, repair or replace the electrode.