THE REDOX POTENTIAL (ORP) IN AQUARIUMS & PONDS;
Effect of Water Changes, DOC, UV Sterilization, Mineralization on a Healthy Redox Balance
(1) Basics (over view)
(3) Natural Redox
(5) Redox as it pertains to Aquariums
(6) Effect of Stress|
(7) Healthy Redox Methods
(8) Redox Problems
(10) Downloadable version of this article
By Carl Strohmeyer-PAMR 35+ years experience
Although not a well known process among many aquarists, with much misunderstanding of both sides of the equation by even some advanced aquarium keepers; the implications of Redox for a healthy aquarium are quite far reaching, and thus important for any aquarist considering moving from basic aquarium keeping (or pond) to advanced to understand.
Even the average aquarist should consider this water parameter when all other parameters check out, yet fish continue to be susceptible to disease. This may be an important parameter to consider as growing research in human disease resistance, and even plant growth also continues to show as research progresses.
As research grows, knowing what can affect oxidation and reduction which are both important in their own way can help an aquarium keeper deal better with sick fish or an aquarium that has a sudden build up of organics. Even lighting and quality of light is showing to have an affect on Redox based on tests!
However some in the aquarium keeping community still seem to be in the dark as per this growing documented research.
Redox, also known as Redox Potential, oxidation potential, & ORP (oxidation reduction 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 ability to gain electrons, many minerals cannot be absorbed and properly assimilated, especially in times of stress.
So it is very important to keep a healthy Redox Balance via proper dissolved oxygen levels, proper positively charged mineral levels (such as Calcium and Magnesium), and even level 1 or higher UV Sterilization.
It is also noteworthy that there is a correlation between Redox Potential and pH (Reference: University of Florida; Biochemistry of Wetlands)
(Please click on the picture above/right to enlarge for a better view)
Many in the past have stated exact numbers are the "best" Redox reading for an aquarium (myself included in the past). My research has found this to be incorrect.
In some aquariums, a higher Redox of 350 mV may be a good Redox to obtain (for oxidation) when high organics and decomposition is lowering water quality.
HOWEVER for a new or established aquarium that is properly functioning this is not a number you should be necessarily "shooting" for correct Redox balance, so please read on!.
*Oxidation describes the loss of an electron by a molecule, atom or ion.
Another way to look at this is to lose, or cause to lose, hydrogen atoms.
EXAMPLE: Redox processes such as the oxidation of carbon to yield carbon dioxide.
Oxidation is the LACK of electrons by a molecule.
Oxidation is when the molecule can accept electrons from a reduced molecule, thus oxidizing.
*Reduction describes the gain of an electron by a molecule, atom or ion.
Another way to look at this is remove oxygen atoms or add hydrogen atoms.
EXAMPLE: The reduction of carbon by hydrogen to yield methane (CH4).
Reduction is the GAIN of electrons by a molecule.
Reduction is when a molecule can give positive electrons to an oxidized molecule, thus ceasing the oxidation of the molecule.
Another example: Calcium (Ca2+) or Magnesium (Mg2+) which initially are composed of two positively charged ions immersed in a sea of movable electrons may have given up all possible electrons to cells/molecules under oxidation.
It is for this reason, then that positively charged calcium and magnesium supplies must be constantly renewed; without this “fresh” positively charged calcium, etc. your Redox balance will suffer.
Think of it this way; a battery "works" only when a positive and a negative electrode are present to maintain an electrical current. When the positive plates become exhausted, the battery is no longer functional, even though the metal plates and other "ingredients" for the battery are still present.
So it is that your GH or Calcium Test may show adequate minerals, but these minerals have been oxidized and thus rendering the test inaccurate as per ESSENTIAL positively charged calcium ions. This why it is folly to attempt to drive down GH to very low levels in a misguided attempt to replicate certain environmental biotopes based on old school opinions of GH.
The above are over simplifications of the process, so please read on as I will go into further depth as the article progresses, especially as Redox relates to aquatic health.
Oxidized water with its Redox potential of +700 to +800 mV* is an oxidizing agent that can withdraw electrons from bacteria and kill it. The oxidized water can be used to clean hands, sterilize utensils, and treat minor wounds.
This is why products such as Melafix which is an oxidizer (albeit mild), is effective at sterilizing a wounds or similar *mV = Millivolts or 1/1000 of a volt of water conductivity
Here are a few oxidizers: ozone (O3; Oxidation potential= +2.1), hydrogen peroxide(H2O2; Oxidation potential= +1.82), chlorine (Cl2) and chloramines (NH2Cl).
Further Reference: Hydrogen Peroxide; Aquarium Medications Part 3
As well, some aquarium products are also oxidizers such as Potassium Permanganate (sold in products such as "Jungle/Tetra Clear Water") and Mardel Maracyn Oxy. For this reason both of these products should be used with great caution in your aquarium (although use in established aquariums with a balanced Redox should not be problem when used as directed).
Even mild oxidizing aquarium remedies such as Melafix or Herbtana should be used sparingly as over use WILL CAUSE oxidative stress, as this is what an oxidizer does, it causes stress to tissues! Think stomach acid, an oxidizer, but you sure would not want your other body tissues exposed to it.
Product Resource: Maracyn Oxy from AAP
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.
Please note that the oxidizers have a plus and the reducers have a negative in the chart to the left. Click graph to enlarge
Here are a few reducers, in other words, elements or processes that can transfer electrons to another substance; Magnesium, Calcium, Sodium, and the process of Photosynthesis involves both oxidation and reducing.
As one can see from the graph, elements such as most metals, as well as essential elements for aquatic life: Calcium and Magnesium are major reducers.
However because of this they are also most easily depleted (the elements at the top and the bottom of the graph are most easily depleted in their oxidation or reducing properties).
Most aquarium water conditioners are also Redox Reducers, albeit very short term/temporary reducers. Examples include SeaChem Prime, Tetra/Jungle Start Right, Kordon Novaqua, and many more.
Further Reference: Aquarium Water Conditioners Review & Information
True UVC Sterilization also reduces, by electrically charging (adding an electron) and breaking down oxidizers in the water column.
The problem of late is the flood on low cost UV Sterilizers or low output medium pressure UV replacement bulbs sold on Amazon, eBay, and other websites that are at best only capable of clarification and NOT true level one sterilization which can then improve Redox balance.
Aquarium Lighting and the "quality" of this light has also in recent preliminary tests shown to reduce Redox, which has important aquarium keeping implications (both positive and negative, depending upon what is currently happening in an aquarium). See the Aquarium Redox section for more.
Simple Test to Understand Redox: Take an 8 oz. glass of water, then add enough Potassium Permanganate to change the color to a mild red, then take any aquarium water conditioner such as Prime or Start Right and slowly add drops to the water and watch the red be "reduced" (neutralized) to a clear brown color.
What you are observing is the reduction of an oxidizer (potassium Permanganate) by a Reducer (generally Sodium Thiosulfate is used in these conditioners).
*Potassium Permanganate (Jungle Clear Water)
*Jungle Start Right
For those looking for an advanced Redox Test, that provides actual numbers in high accuracy:
*EcoSense ORP 15 Redox Meter
An important note, is that although oxidation is a necessary part of biochemistry for fish and all animals (such as for energy production), the NORMAL HEALTHY state is one of reduction.
During normal biochemical processes molecules that are normally reducers give up their electrons (in much the same way a car battery does until re-charged), so without a recharging via the addition of new minerals that are high in these electrons or even processes such as UVC sterilization (or even high PAR lighting), your aquatic biochemistry will suffer and eventually so will your fish!
*UV Sterilization; Complete Facts & Information
*Aquarium Lighting; PAR
One more basic generalization to consider before moving into more depth is this: Water that is of low pH (acid), in general, measures high ORP while water of high pH (alkaline) measures low ORP (please note that this is a broad generalization).
However, in natural water (generally spring water), acidity of minus ions and alkalinity of plus ions can coexist (more about this in Natural Redox).
See this website for more; Understanding pH and ORP
As a final note, 2012 human research has shown that an intake of 75% alkaline foods versus 25% acid foods are best for essential Redox Balance. While this is not a perfect comparison, sine the human body changes the pH of food as it progresses from the stomach into the small intestine, this can still be reasonably extrapolated to fish in the the water environment and foods should allow for this as well since the physiology of fish and humans are similar. As well since fish live in their liquid environment, water parameters such as Redox have a more definite affect on fish than with humans.
This of course often confounds those who constantly dump copious amounts of acid buffers or similar in their aquarium or worry about a generally fictitious "too high GH".
This picture/graphic below explains some basics of Redox:
It is important to note that Aquarium Redox can be a complex subject with some basic principles to also understand, however reading one section of this article will yield incomplete information. For this reason I recommend reading the whole article (as well as links provided) for a more thorough understanding. It may take more than one reading as well.
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My research and interest in Redox goes back to my curiosity as to why certain aquarium maintenance methods were more effective in keeping healthy fish, and the common knowledge of the day did not fully explain results I was achieving.
I base this article on Redox studies as it corresponds to humans and all fish, animals, and even plants.
I have found from practical experience and research that a lot more can be learned from medical studies or other university level studies than from many aquarium articles and sadly some otherwise excellent forums (these articles/forums usually just take bits from another article without any real research, often with old ideas being simply regurgitated).
Originally my statement on Redox was: "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.
The more I have studied this subject as well as the newest research shows that all aquarists should have at least a basic understanding of this subject as it has major implications for fish and aquatic health that often go against commonly held aquarium keeping beliefs.
I have also changed my opinions about this subject based on newer evidence about a balanced Redox.
One such opinion 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 and simply repeating what I was told, but newer human research and my own tests over the last 15 plus years have lead me to where I am now, that a BALANCED Redox is important.
What is a balanced Redox? The best research indicates a Redox that can respond to both the oxidation and reduction needs of the environment and more importantly the fish or other aquarium inhabitant. This can be a reading between +300 to -200 mV (a higher Redox is sometimes needed when oxidation is necessary due to high organic de-composition)
See the chart below (ecologically safe water):
Maintaining a proper Redox Balance (or Potential) which includes the reducing side of the equation is a lot like having an anti-oxidant vitamin in the aquarium water (although a more accurate description would be magnetically charged 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” .
Looking at the oxidizing side of the Redox equation; Bleach and Potassium Permanganate are oxidizers (Potassium Permanganate is often used for disease treatment and water clarification in ponds and aquariums). However you would not want your fish living in a constantly oxidizing environment for long term fish health, rather you would want your fish in a balanced redox environment which includes a Reducing environment where free radicals are not damaging the cells of your fish and causing problems with Osmoregulation.
Further Information: Fish Osmoregulation
An oxidizing environment is what you get with a positive Redox of generally +350 mV and is OK (& necessary) for certain periods such as during disease treatments, however you would not want to keep your fish in constant medication any more than in a constant strongly oxidizing environment (PLEASE read the section about Natural Redox including the quote and outside Redox for a better understanding of this concept)!
Another IMPORTANT consideration is a healthy Redox affects the electrolyte balance in your aquarium. Calcium as well as Magnesium are both important reducers when positively charged, however they are both easily oxidized as well (please see the chart in the Redox Potential Basics section).
So for proper reduction, these elements, or at least their positive ion charge need to be replaced on a constant basis (read further in this article for more on this subject).
The Redox Potential explains a lot of the results I was getting as the fish have a better ability to resist a disease sometimes simply by having a healthier immune system and osmoregulation.
This pertains to a Balanced Redox potential (which includes a proper magnetic charge in the water) that I have found a properly installed and constructed UV Sterilizer aids in maintaining as well as proper mineralization of reducers and constant replenishment of these minerals, such as calcium, and regular water changes. that lower nitric acid and DOC levels (dissolved organic compounds).
Further Reference: Aquarium Cleaning, reasons, methods
What got me started in researching this topic was that I noticed and documented, differences in health, vitality and especially disease resistance within different aquariums.
I noted a difference in health with very regular small water changes or flow through water change methods, UV sterilizers, and added minerals/ electrolytes (such as Wonder Shells or similar methods/products). This improvement/difference was noted over tanks kept with more traditional methods such as "Amazon" biotopes where RO water was used and no replacement mineralization (Cation replacement) was used on an on going basis.
I mostly used goldfish for these tests. The goldfish had fewer instances of general diseases as well as infestations such as Ich, Anchor Worms, and other problems with the constant replenishment of mineral cations and the use of correctly installed efficient UV sterilizers which contribute to balanced Redox.
What is/was noteworthy is that the UV Sterilizers were not even run within the parameters that would kill Ich outright, yet I still was observing lower instances of Ich!!
WHY? The answer is simple in that the aquarium had a more healthy Redox Balance that aided in the fish' own natural immunity and resistance to Ich!
PLEASE NOTE; many UV Sterilizers now marketed for under $50 CANNOT perform Redox reduction due to their poor dwell time, low cost medium pressure UV bulbs, and other factors, these are at best clarifiers and should NEVER be purchased unless that is all you desire from your UV!.
Further Reference: Actual UV-C Emission from a UV Bulb
This shows that the health of aquarium fish can be directly aided by positive mineral ions/magnetic charge of the water and a properly installed "true" UV Sterilizer, not just by the killing of potential disease pathogens, but also by the effect UVC has on the Redox Balance of an aquarium.
I have been observing many aquariums of "ordinary" fish, 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 (such as mineralization and water changes) that had a UV Sterilizer installed, were generally much healthier.
A High Dwell Time UV Sterilizer works similar to the ozone layer in our upper atmosphere (except in reverse); although the UVC emitted by the sterilizer is itself an oxidizer, the interaction of the UVC inside the unit with oxidizers such as ozone is such that the UV Sterilizer REDUCES these oxidizers and free radicals as well as potentially magnetically charges the water.
This was confirmed by Dr. Mamoon Kundi in an email he sent me as per his work using UVC to balance Redox in human studies, and thus improving immune function
Product Resource: TMC Vecton & Advantage "High Dwell Time" UV Sterilizers
For those interested in checking this out, simply add potassium Permanganate into a tank with a UV Sterilizer and one without. The tank with the UV Sterilizer clears MUCH quicker!
If your aquarium has a high bio load, the addition of a properly installed UV Sterilizer can actually temporarily add too much Redox Reduction resulting in a darkening of water color until the Aquarium Redox balances again.
Please Reference/Read: Aquarium Bio Load
Unfortunately the aspect of Redox Balance and Ultra Violet Sterilization is often missed my many aquarists, and sadly many otherwise well informed reef keepers.
Further Reference: UVC Sterilization/Sterilizers and the effect on a Healthy Redox
See this outside article for UVC/UVB healing therapies in humans now being proven in tests! Oxygen Healing Therapies with UVC
In further research I noted that 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 as Vitamin C, and many others.
In medical studies, the enhanced oxidizing environment can facilitate the binding of pathogens or antigens to effector cells (a type of lymphocyte that are actively engaged in secreting antibodies) leading to a hyper-responsive innate immune system.
Previous work has shown that an oxidizing environment leads to enhanced release of super-oxide and nitric oxide, activation and translocation of nuclear transcription factor and enhanced production of cytokines (proteins and peptides that are signaling compounds produced by animal cells to communicate with one another).
The creation of a reduced environment by addition of antioxidants blunts all of the above primary responses of the innate immune system.
Back to my many tests with goldfish tanks over several years in the 1990s; I ran these tests with many different filters and combinations there of.
Cleanings were consistent every two weeks with about 25% changes of water via a Gravel Vacuum. Feeding was performed at the same intervals with the same food (at that time Hikari and Spirulina 20), and all the tanks had the same number of goldfish at as close to the same size as possible.
I found the tanks with the Under Gravel Filters performed the worst (and not just in Redox) due to their tendency for DOC (Dissolved Organic Compound) buildup which results in high amounts of Nitric Acid production.
UG Filters performed better when combined with a UV Sterilizer and another filter such as a canister filter, however the tanks that performed the best did not have UG filters, rather a combination of two filters (generally a Sponge Filter or Fluidized Filter were part of this combination) AND a UV Sterilizer.
*Aquarium Sponge Filters
*TMC premium 3rd generation Fluidized Sand Bed Filters
Some of the tanks were maintained with added minerals/electrolytes, some were not.
The best results as per long term health were achieved where minerals cations (positive mineral ions) were added on a constant basis vs. methods that required weekly or similar dosing requirements or non minerals at all.
That said, please read the rest of the article before I over sell any one on a UV Sterilizer, Mineral Blocks (such as AAP Wonder Shells), or drip mineral applicators (products such as SeaChem Replenish can be mixed with water and dripped into the aquarium). As often good aquatic husbandry is a major factor in a healthy Redox Potential (balance).
Another interesting aspect of Redox potential is the correlation of a certain Redox level and the growth of Blue Green Algae (Cyanobacteria) in Aquariums and lakes. This is an on-going study however Redox does SEEM to play some role in the aquarium and lake “plague”.
For more information about this, I recommend reading this article:
Blue Green Algae (Cyanobacteria) in Aquariums; what it is and how to control it.
Currently this is just an opinion/theory though.
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NATURAL REDOX Including Human Studies:
Over geologic time, abiogenic, biogenic, and anthropogenic deposits were accumulated in rivers, lakes and seas.
I have mostly discussed Redox Reduction and its misunderstood importance, however there does need to be a balance between reduction and oxidation for proper chemistry within a fish or most all living animal organisms.
REDOX POTENTIAL (BALANCE) AS IT PERTAINS TO AQUARIUMS:
There are multiple mechanisms for maintaining a good redox balance from a good oxygen exchange for oxidation to mineral ions and certain light energy for important reduction.
Important; what is often missed, is that although you may test and, for instance find, high calcium levels in an aquarium via a GH over 300, this does not necessarily mean you have any Redox reduction as I should point out that very basic fact of Redox reduction is the donor (such as calcium) transfers electrons to another substance, and is thus, oxidized itself.
Put another way, there is certainly a time and place for a high Redox (oxidation) as lower oxygen levels from many causes such as high organic decomposition is generally not desirable and this will lower your Redox oxidation side of the equation.
This is not what I recommend as a means of a reducing Redox environment. However to not have the proper reducers or creating a highly oxidative environment is also not good for long term fish health.
The Redox Potential is always going to be in flux and as yet no scientific equilibrium has been established here.
Maintaining reducers such as Calcium and Magnesium in your aquarium is just as important as proper levels of dissolved oxygen (which raises Redox).
There is evidence both anecdotal and controlled that proper levels of calcium and other anti-oxidants such as Vitamin C (along with other healthy water parameters) will prevent and even cure Hole in the Head disease (HITH). Redox is an important parameter here.
Further Reference: Aquarium Answers, about Hole in the Head Disease
As stated earlier, Redox can be more important than pH, there are definitely correlations to pH and the Redox effect on pH.
But you cannot make the assumption that if you have a pH of 8.0, that you have good reduction. Just like with GH, where your GH is high, you can still have low pH.
The bottom line is that there are relations between Redox, GH, pH, and even kH, but these are still individual water parameters.
Also as noted in the beginning of this article, this is not a parameter to stress over, HOWEVER, Redox reduction should NOT be blown off as many anecdotal/uninformed commentators do in some aquatic forums. The more I have studied and observed in this subject, the more I feel it should not be ignored!
Effect on Fish:
Active oxygen molecules, or free radicals, are produced in the water and the fish’ body. They are extremely reactive and can also attach themselves to normal, healthy cells and damage them genetically.
These active oxygen radicals steal electrons from normal, healthy biological molecules.
This electron theft by active oxygen oxidizes tissue and can cause disease; these are proven facts!
This why the constant hammering by some un-informed aquarists (such a popular planted aquarium guru) against UVs, too high a GH (which is not always a good indicator of electrolyte balance anyway), and even the use of mineral blocks (such as Wonder Shells) is ludicrous!
Your GH may test higher than desired but in actuality is maintaining a healthy Reducing Redox via the reducing properties of positively charged calcium, magnesium, etc.
Further Reference about Calcium: Calcium (Facts about Calcium, an essential reducer)
Human studies show a clear link between the Redox level in the blood of a healthy person and an unhealthy person, especially when it comes to cancer. Those with cancer and other chronic illnesses show more oxidation.
For fish, this means that while oxidizing agents have their place, we should not be regularly dumping oxidizing products in our aquariums, even if they are so-called "natural" products whether it be Microbe-Lift Herbtana or API Melafix. The scientific facts are that over the long term the regular use of these products WILL SHORTEN the life of your fish and make them more susceptible to diseases, including tumors.
Reference: Tissue redox activity as a hallmark of carcinogenesis
Effect on plants:
In a controlled test conducted with terrestrial plants; plants treated with magnetized water (basically Redox Balanced Water) reacted in a test, with a growth in the order of 20% to 40% bigger than the plants treated with regular water.
While no test has been conducted with planted aquariums, it is not rocket science to draw conclusions from this study and apply this to a planted freshwater aquarium and the effect of Redox Balance on plant growth!
Reference: Water Information & Conductivity
Simple Redox Test
A simple test of Redox can be performed using Methylene Blue and any reducer such as powdered Wonder Shell.
Simply add enough Methylene Blue 8 oz. of water to turn the water a brilliant blue (usually one drop).
Then add about ½ teaspoon powdered Wonder Shell to the 8 oz. of water and stir. The Methylene Blue will dissipate due to the reducer.
Taking this test a step further into the real world; again add enough Methylene Blue 8 oz. of water to turn the water a brilliant blue (again one drop), this will be the control color. Then take out 8 oz. of aquarium water and add the same amount of Methylene Blue as in the control glass of water.
If the color dissipates at all (even the slightest) you probably have a balanced Redox with at least some reduction. Expect to see little color change in a healthy aquarium, although absolutely no color change MAY indicate too much oxidation, while any more than a subtle change may indicate too much reduction.
More about Methylene Blue: Aquarium Medications Part 3, Methylene Blue
For a more scientific Redox measurement device:
EcoSense ORP 15 Redox Meter
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REDOX AS IT PERTAINS TO STRESS
In biological systems, the Redox Potential must be kept reduced to perpetuate the life process. In other words, the concentration of DHA (an oxidized form of ascorbic acid), must be kept to a minimum.
Healthy Redox Potential (Balance) maintenance methods:
For Redox problems, possible problems:
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This is a relatively unexplored area of fish keeping, and there is still a lot to be learned here and I have to admit having to change my opinions based on newer evidence (I too thought that ONLY a high positive Redox should be maintained), my research is still ongoing and I try and read whatever I can on this subject, especially from outside the aquarium hobby, even if it may not fit with theories I hold.
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