Testing for ORP with Potassium Permanganate
Editor’s Note: The instructions below, which we’ve modified a bit, were prepared by the original manufacturer of Filox-R iron removal media. The purpose is to provide a quick and easy way to determine if your water can be treated by standard manganese dioxide-based iron filter media like Filox without the use of additional oxidizers like chlorine, air, ozone, hydrogen peroxide or potassium permanganate.
Oxidation Reduction Potential (ORP) can be the most important factor to take into consideration in certain waters. Highly reducing waters may cause premature exhaustion or even destruction of the Filox-R bed.
Precautions can be taken prior to installation that can prevent ORP problems. Use one of the screening tests and follow the instructions below if the subject water has reducing properties that will require additional oxidants.
The Simple Test
Mix 1.75 ounces (50 grams) water with 0.75 ounces (22 grams) of potassium permanganate crystals. Then take 2 drops of the mixture and stir into a fresh ¼ gallon (1 liter) sample of the subject water. Let the subject water stand for 15 minutes. If the pink color remains, Filox-R can be installed without additional oxidants. If the pink color disappears, additional oxidants will be needed for Filox-R to function properly.
The ORP Test with a Meter
Note: Must use a calibrated ORP meter. Any reading that is above a negative 170 millivolts indicates that Filox-R can be used effectively without additional oxidants. Any reading falling below a negative 170 millivolts indicates that additional oxidants will be required.
The amount of oxidant required for proper installation can be determined by measuring the amount of oxidant added to a specific volume of subject water until the solution remains pink or the meter reads at negative 170 millivolts or above. An extrapolation can then be made to determine the correct feed rate for the oxidant with respect to the subject water flow rate. Once installed, sample the solution after the injector and mixer and repeat the above test to confirm that the feed rate is correct.