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First Stop Aquatics > pH - ORP Monitors > ORP Monitors
The ORP (Oxidation Reduction Potential) or redox potential relates to the degree of water purity in the aquarium. It is a measuring value (millivolts of conductivity) that gives information about the reduction and oxidation characteristics of water. (Redox is a contraction of reduction-oxidation.) Redox potentials are closely related to the stability of the aquarium and is often used as a 'barometer' of water quality.
Agents that contribute to poor water quality decrease the oxygen content of water. These are reductive agents and include organic compounds (e.g. food, feces, mulm, etc.) which rapidly decompose to toxic compounds like ammonia and nitrite. Reductive agents decrease the redox potential, indicating the deterioration of water quality.
Oxygen and ozone are oxidative agents. They are important to water quality not only for respiration requirements but because they are able to offset the negative effects of the reductive agents.
Maintaining animals in an aquarium naturally tends to lower the redox potential. (Ammonia, nitrite, carbon dioxide, sulfides, etc., all tend to lower the redox potential).
Ozone is a strong oxidizing agent and its use can maintain the desired redox level in the aquarium. Studies show that increasing the redox potential from 200 mv to 300 mv in 100 ml. of water will reduce the concentration of coliform bacteria from 300 ppm to 30 ppm, a 90% decrease. Increasing the redox potential from 200 mv. to 400 mv. in 100 ml. of water will reduce the concentration of coliform bacteria from 300 ppm to 3 ppm, a 99% decrease.
Generally a ORP reading of between 350-450 mv is recomended for marine aquariums and between 300-400 mv for freshwater systems and ponds.
