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Aquarium Redox Potential - by Carl Strohmeyer


This article is based on studies about the Redox Potential as it corresponds to humans and all fish and animals. I have found from practical experience and research that a lot more can be learned from medical studies than from many anecdotal aquarium articles, this is not to say that this research then has to be properly applied and a good aquatic article helps here.
I do not believe this is a subject that many aquarists should stress over, but a lot has been learned about this subject since I first started researching this in the 1980s. I have also had to change my opinions about this subject based on newer evidence. One was should you have a positive or reducing Redox. I based my earlier opinion on a higher Redox of 300 mV based on many studies of ocean waters, but newer human research and my own tests over the last 10 years have lead me to the fact a Blance of both Reducing and oxidizing Redox is essential.

All this said, maintaining a good Reducing Redox (especially in Freshwater) can be as simple as good aquatic husbandry: water changes, proper electrolytes and minor elements in the water, and simple reducers such as Sodium Thiosulfate.

Put another way, maintaining a proper Redox Potential is a lot like having an anti-oxidant vitamin in the aquarium water. The Aquarium Redox is also just one more parameter towards good disease prevention and long term fish health and growth. Please see this article about Aquarium Disease prevention;
“Aquarium Disease Prevention”

What got me started researching this was I have noticed and documented differences with aquariums (I mostly used goldfish for these tests) with UV sterilizers, added minor elements and electrolytes maintaining a Redox Potential that was both oxidizing AND reducing at times, but was not sure why health, vitality and especially disease resistance were improved. The goldfish had less incidence of such infestations as anchor worms which UV sterilizers cannot truly eradicate due to difficulty killing them in the UV itself and that Anchor Worms do not get readily caught up in the water column. The Redox Potential explains a lot of the results I was getting.
This pertains to the Redox potential of -200 -+300 mV that I have found a properly installed and constructed UV aids in maintaining (assuming proper dissolved oxygen levels, and proper mineral levels too, such as kH ). A proper Redox Potential improves the health of humans AND fish. A Redox Potential in the -200-400 mV range in human studies has been shown to have the same affect as anti-oxidant preparations such Vitamin C (and many others). This shows that the health of aquarium fish can be maintained by a UV Sterilizer not just by the killing of potential disease pathogens, but by the maintenance of a proper Redox Potential. I have been observing many aquariums of such "ordinary" fish as goldfish, both with and without UV Sterilizers (keep in mind that some UVs are useless by design and installation), and the goldfish with every other factor equal that had a UV Sterilizer installed, were generally much healthier.

I will also note that the aquariums with the proper Redox had the electrolytes present as tested via GH & KH (salt,
Marine Buffer, & Wonder Shells are a good source), and regular water changes which also resulted in lower nitrate levels (40 ppm or less for FW, 20 ppm or less for SW)

That all said, please read the rest of the article before I over sell any one on a UV Sterilizer or Wonder Shells. As often good aquatic husbandry is all that is necessary for a good Redox Reducing environment.


Redox Potential (oxidation potential) describes the ability for the loss of an electron by a molecule, atom or ion to the gain of an electron by another molecule, atom or ion. Without this positive Redox Potential many minerals cannot be absorbed and properly assimilated. So it is very important to keep a proper Redox Potential (-300 to -350mV) via proper dissolved oxygen levels, UV Sterilization, and proper electrolyte levels (such as magnesium).

Oxidation describes the loss of an electron by a molecule, atom or ion
Reduction describes the gain of an electron by a molecule, atom or ion
The above is a simplification of the process, and much more needs to be considered, please read on.

Reduced Water:
Reduced Ionized with a Redox Potential of -250 to -350 mV readily donates its electrons to unusual oxygen radicals and blocks the interaction of the active oxygen with normal molecules. Substances which have the ability to counteract active oxygen by supplying electrons are called scavengers. Reduced water, therefore, can be called scavenging water. Reduced water inhibits excessive fermentation by reducing indirectly metabolites.

For my full article which includes natural Redox and how Redox pertains to Aquariums, please follow this link: http://www.americanaquariumproducts.com/Redox_Potential.html

Professional aquarium maintenance experience since 1978 as the owner of one of the larger aquarium maintenance companies in LA, CA.

I have been in the hobby since 1969.



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