Redox

About Redox
The ORP (Oxidation Reduction Potential) or redox potential relates to the degree of water purity in the aquarium. It is a measuring value (millivolts) 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 +300 to -100 mV is recomended for marine aquariums and between +125 to -200 mV for freshwater systems and ponds.

Redox is also related to the Biological Oxygen Demand (BOD).

An acceptable BOD value is at about 1–2 mg/l (ppm).

There still is no conclusive proof on this subject as yet that ORP only climbs on total purity of the water. Extremely complex and unknown water chemistry questions still exists unanswered for now.

Redox and Algae
Each species of algae reacts differently to changes in the redox potential. Generally, high redox potentials support the growth of green algae and suppress brown and red algae.

Measuring Redox
You can measure the redox potential of a sample of water by the use of a calibrated electronic Redox probe.

Links

 * ORP by Wikipedia
 * Redox by The Krib
 * Oxygen by Algone Corp.
 * The Redox Potential In Aquariums (And Ponds) And How It Relates To Proper Aquatic Health