THE REDOX POTENTIAL (ORP & rH) IN AQUARIUMS & PONDS;
Effect of Water Changes, DOC, UV Sterilization, Mineralization on a Healthy Redox Balance
(1) Basics (over view)
(2) Relative Hydrogen (rH)
(4) Natural Redox
(6) Redox as it pertains to Aquariums
(7) Effect of Stress|
(8) Healthy Redox Methods
(9) Redox Problems
(11) Downloadable version of this article
By Carl Strohmeyer-PAMR 35+ years experience (with input and proof reading by others, including experts in this field) Updated 4/11/18 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, especially now with peer reviewed research into the correlation of rH, 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. 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. So it is very important to keep a healthy Redox Balance via both sides of the Redox equation; It is also noteworthy that there is a correlation between Redox Potential and pH (Reference: University of Florida; Biochemistry of Wetlands) The video below shows some of the correlation of pH and Redox: Redox also relates to water changes and the amount/frequency there of. We should note that we have both slow and fast Redox reducers and slow and fast Redox oxidizers.
Generally in a healthy aquarium regular use of "fast" oxidizers or reducers is not necessary (which the exception of occasional water conditioner use for chlorine reduction). Fast reducers or oxidizers also generally are relatively temporary, although chloramines are definitely a fast reducer that is not temporary. Examples include:
ALL INFORMATION contained here in is copyrighted research and may only be used with permission, in particular to promote products for sale outside of AAP.
REDOX (REDOX POTENTIAL) BASICS (OXIDATION POTENTIAL, ORP):
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.
Without this ability to gain electrons, many minerals cannot be absorbed and properly assimilated, especially in times of stress.
(a) Normal oxidizers such as proper/optimum dissolved oxygen levels
(b) To counter oxidative stress (often artificially induced in our aquariums); via proper positively charged mineral levels (such as Calcium and Magnesium) and even level 1 or higher UV Sterilization.
Fish Health- Quick pH/Redox Demonstration
This article has information about using Potassium Permanganate in a very simple (& fun) test to determine the health of your aquarium before and after a water change:
Aquarium Cleaning; Reasons (See Redox Section)
This is a good reason to not use these products as a disease prevention tool (as many mistakenly do with Herbtana and Artemiss), only for occasional treatment use or at least in balance with products such as AAP Wonder Shells.
Purigen and especially Chemipure along with "The Poly Filter Pad" are more "medium" oxidizers so extra care should be exercised with their use.
This does NOT mean you should not use Purigen or Poly Pads, just be aware of this important negative side to Redox and counter these with AAP Wonder Shells or similar mineral reducers that are added slowly.
By Carl Strohmeyer-PAMR 35+ years experience (with input and proof reading by others, including experts in this field)
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, especially now with peer reviewed research into the correlation of rH, 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.
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.
So it is very important to keep a healthy Redox Balance via both sides of the Redox equation;
It is also noteworthy that there is a correlation between Redox Potential and pH (Reference: University of Florida; Biochemistry of Wetlands)
The video below shows some of the correlation of pH and Redox:
Redox also relates to water changes and the amount/frequency there of.
We should note that we have both slow and fast Redox reducers and slow and fast Redox oxidizers. Generally in a healthy aquarium regular use of "fast" oxidizers or reducers is not necessary (which the exception of occasional water conditioner use for chlorine reduction). Fast reducers or oxidizers also generally are relatively temporary, although chloramines are definitely a fast reducer that is not temporary.
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.
Here is an excellent article further explaining how a battery works as it relates to Redox, both oxidation and reduction, and both Anodes and Cathodes (think Anions and Cations).
This also explains why a mineral "salt such as CaCO3 (Calcium Carbonate) can have a positive (Cation) ion charge.
Basics of Electrochemistry
What is noteworthy in reading the above article is it speaks of an ionic solution, which our aquarium water is not quite the same as a battery here (saltwater is more so than freshwater), however this also points out the importance of not using totally neutral distilled/de-ionized water to house your fish, as then there is definitely no ionic solution for this current.
QUOTE from the above cited reference/article: "Ions in solution will move from an area of high energy toward an area of low energy producing, a current".
Where the battery comparisons further work, especially for the nay-sayers who claim "we are only measuring ions with a GH test", is that as the calcium Cations are used up, the calcium tends to bind to anything in the aquarium, from objects to even coral in reef aquariums. I have observed this 100s of times (if not 1000s).
Similar to this action in a battery:
QUOTE: "When the lead acid battery accepts charge, the sulfuric acid gets heavier, causing the specific gravity (SG) to increase. As the SoC decreases through discharge, the sulfuric acid removes itself from the electrolyte and binds to the plate, forming lead sulfate."
Reference: How to Measure State-of-charge
It is also noteworthy that while a TDS meter is a good device for any advanced aquarium keeper to own, a TDS meter measures conductivity and pretty much everything that is in the aquarium water, thus not necessarily measuring GH (& KH for other reasons) which COULD could be a mistake as reducing Calcium Cations could still be low.
If you are really looking to "go pro" definitely own a good TDS Meter (such as the AAP/TMC) ALONG WITH a good ORP/pH Meter (and of course some basic GH & KH test kits too).
Reference: Aquarium Chemistry; TDS
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. This is clearly demonstrated by picture later in the Aquarium Redox Section of this article.
The problem of late is the flood on low cost UV Sterilizers and/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 (or at the most perform this action poorly).
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).
For those looking for an advanced Redox Test, that provides actual numbers in high accuracy:
*EcoSense ORP 15 Redox Meter
Or an even more advanced test by Hanna Instruments:
*Hanna ORP, PH, Temperature Meter #H198121
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!
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
Also worthy of note, a 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".
RELATIVE HYDROGEN (or rH):
This section on rH compliments of Rogier Van Vlissingen.
This takes ORP reading a step further as to showing the true health of the water.
The rH/Relative Hydrogen Score, is a better measure of whether the water is actually oxidizing or reducing than ORP is. ORP is a proxy, rH directly measures atomic H in the water, (which includes H-), so it is still not a direct measure of H-, but it's closer than ORP.
In 1997 Prof. Sanetaka Shirahata of Kyoto University published a paper in BBRC (a peer reviewed journal, Biolochemical and Biophyscial Research Communications), which demonstrated for the first time that H- persisted in electrolyzed water, putting to rest an industry myth that the reason for the health effects of the alkaline water from electrolysis was the very alkalinity of it. Not so, it was the presence of H-, which science up to that point had believed could not exist but for nano seconds.
Dr. Hidemitsu Hayashi pointed out that in several natural bodies of water the same thing was found, and he began manufacturing his mineral sticks, which were a much cheaper and more effective way to create HRW, hydrogen rich water. As per my history section later in this article, it was in part the use of Cation rich mineral blocks that I myself stumbled upon this concept after observing improved fish health.
FURTHER (Quote from The Relative Hydrogen Score, aka the rH Score):
The rH scale employs the same logarithmic Bar scale used to express gas pressure in terms of order of magnitude, and the rH scale runs from 0 to 42; 28 is mid-point (balance), below 28 is reducing, above 28 oxidizing... Therefore, an rH score of 0 would indicate maximum possible reducing (antioxidant) power, while a score of 42 would indicate the maximum possible oxidizing environment.
So, rH yields a hydrogen proton-unbiased measure of absolute reducing potential of a substance; eliminating effects due to pH. rH is log1/hydrogen partial pressure; a one unit change in rH indicates a 10X change. E.g., a shift on the Barr scale of rH from a score of 27 to one of 26 indicates a 10X increase in reducing power. rH 28 = H partial pressure (pp) of 10^-28 atmospheres, an rH 11 = H pp is 10^-11 atmospheres, and a 0 rH is the rH value of pure hydrogen at STP. Again, as noted above, an rH score of 0 would indicate maximum possible reducing (aka “antioxidant”) power, while a score of 42 would indicate the maximum possible oxidizing environment.
Nonetheless, ORP and better, rH, have found some degree of acceptance for many years in the fields of high-end aquarium keeping, wine and beer brewing, food storage and food safety as an indicator or relative antioxidant ability, and, since the mid-to-late 90's; in some sectors of the nutritional antioxidant field as an indicator of the same as well. It is somewhat important to note that ORP and rH scores have also been used to some extent for many years in the groundwater and waste water remediation fields as well as measures of relative oxidation or reducing ability of water.
By keeping track of your measurements with a spreadsheet, you can track rH.
Below 28 on the scale is reducing, above 28 is oxidizing... therefore any rH below 28 indicates anti-oxidant effectiveness of the water by the presence of atomic H, which will include H-.
We are beginning to find healthy aquariums will have rH reading is between 23 & 28 (although as yet an exact number has not been established for marine aquariums, I suspect it is likely 25-30)
You can use a spreadsheet to do the work. The most exact formula is rH=((ORP+205)/29.58)+2*pH), in simplified form it is ((ORP+200)/30)+(2*pH), but I see no reason not to use the accurate formula.
*Everything Aquatic; Redox Results. ORP, PH, rH
*Water Institute, and Munenori KAWAMURA, M.D., Kyowa Medical Clinic
A quote from the above article:
"Since May ’85 we have confirmed thousands of clinical improvements, obtained solely by exchanging drinking (as well as cooking water) from tap water to reduced water."
*Examples of RH Scores Calculated from Various ORP & pH Values
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.
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.
This article is an out-growth of many 1000s of observations and some controlled tests in search of an answer/explanation that commonly held aquarium keeping believes simply could not explain or were even contradictory to (such as commonly held views about GH in freshwater aquariums as well as the effect of UVC on all aquariums as per disease resistance). As I research this subject more and more, I find that it answers many of these results, but I am still learning too as I am already finding out more to Redox than just mineral Cations and oxidation versus reduction such as Relative Hydrogen (rH).
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 often 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.
An example would be HLLE in marine fish where evidence points to a direct link of an oxidizing environment without a constant input of Redox reduction to balance this being a causative factor.
Further Information: Fish Osmoregulation
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..
My many observations in both fresh & saltwater lend to this principle too as to how fish, both freshwater & marine respond both short & long term to oxidizers and/or the lack of a constant source of reduction to balance out oxidative stress.
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.
Back To Top
NATURAL REDOX Including Human Studies:
Over geologic time, abiogenic, biogenic, and anthropogenic deposits were accumulated in rivers, lakes and seas.
Simultaneously all three of these processes proceed to self-purify natural water on the basis of the chemical reactions of oxidation and reduction.
At the initial stages of this natural cycle, toxic hydrophobic organic compounds (molecules that are repelled from a mass of water) are oxidized to the hydrophilic form, which is a molecule, or portion of a molecule, that is typically charge-polarized and capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents.
Energy of oxidation by way of degrading organic compounds is absorbed during reduction chemical transformations. Excess ions of the heavy elements transform into insoluble, inert, nontoxic forms. The concentration of ions of light elements are then stabilized.
Spring waters, which are considered to be the most clean, according to the ecological criteria, are filtered through the rocks and subjected to the oxidation and reduction, sorption and catalytic influence.
ORP can change rapidly, and Redox potentials above 400 mV long term are dangerous to life.
In tests using electrochemical purification, water keeps its initial neutral values of pH, but ORP (Oxidation Reduction Potential) of water shifts toward the negative (electrode or reduction) values.
The above partially explains how a proper Redox Potential improves the health of the fish or other aquatic organisms as I have observed.
Here is a Quote about pH vs. Redox:
A further point on human studies shows this:
Below is a chart that shows Redox Reactions that support life
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.
Bio Chemistry as it relates to Redox Balance:
Free radical chemistry is the underpinning of 2 broad classes of signaling molecules in biological systems: ROS, which are reactive intermediates of oxygen metabolism, and a closely related group of RNS.
Superoxide and other ROS are produced in the mitochondria during oxidative phosphorylation as a normal byproduct of aerobic respiration in fish (and other animals).
The problem begins when either ROS (oxidation) or RNS (Reduction) get out of balance and unfortunately in closed aquarium or pond systems this is all too common.
Reduction is dependant on production of RNS; NOS3 (endothelial NOS) are found in a variety of cell types and are regulated by binding to calcium and calmodulin (calcium-binding protein expressed in all eukaryotic cells).
As well, the reduction side of this equation can also be interrupted by the oxidation of other reducing chemicals such as ascorbate (vitamin C) and reduced thiols, especially glutathione (a tripeptide). These reduced chemicals become temporarily oxidized when they interact (giving up of their free electrons) with oxidizing agents and oxidizing free radicals.
A more basic aspect of Redox Balance is the water we use can have a direct impact as well.
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.
Another way to look at the Redox Potential in aquariums is to the relation of waste particles and acid production, as well as dissolved oxygen and most importantly depletion of key important elements.
You really need to look at the electrolyte balance in your aquarium.
Obviously high organic wastes also require an input of oxidation (higher Redox for Redox balance), but this should not be ongoing due to a poor balance of reducing to oxidation because of the lack of redox reducing mechanisms as well as a bio load the aquariums system cannot support.
The nitrogen cycle requires an input of oxidation, but it also requires an input of reduction due to the excess oxidizers/free electrons (Anions) produced. Without this balance, one creates an environment where the fish could therefore be attacked by these Anions (although a planted aquarium may not suffer from this aspect as much since many plants utilize these nutrients prior to entering the nitrogen cycle). This is also the problem of a high bio load in an aquarium or pond.
The picture to above displays this process
SIMPLY PUT, THESE FACTORS HAVE THE MOST AFFECT IN REDOX BALANCE MAINTENANCE
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.
This again is where many will claim that their calcium or other minerals are high enough or even too high (as many still get INCORRECTLY stressed about the high GH brought on by Wonder Shells, totally missing that these mineral blocks are constantly reducing the water via their donation of electrons!).
With the above statements in mind, one must look at two VERY basic organic chemical reactions that occur in an aquarium;
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.
As stated earlier, Redox can be more important than pH, there are definitely correlations to pH and the Redox effect on pH.
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.
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!
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.
In short, oxidative stress most definitely plays a role in both short & long term fish health and ability to heal. Diseases such as Columnaris and HLLE can be linked to oxidative stress from both my 1000s of observations as well as research.
Effect on plants:
Simple Redox Test
A simple test of Redox can be performed using Methylene Blue and any reducer such as powdered Wonder Shell.
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.
EcoSense ORP 15 Redox Meter
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.
The initial rate at which the redox potential falls as DHA increase is initially slow, however as DHA increases further, the redox potential falls faster, becoming progressively more antagonistic to the metabolic processes of life. Eventually; if the process is not stopped, the fish (or any animal organism) slides down into death.
This is why even prolonged stress can lead to illness and even death and why under stressful conditions having ample reducers such as a constant supply of positively charged calcium ions or TRUE UVC sterilization is so important! Common stressor examples include constant harassment by tank mates, or constant, albeit well meaning use of many treatments meant to cure fish, but that are also Redox Oxidizers.
Healthy Redox Potential (Balance) maintenance methods:
For Redox problems, possible problems:
This was in the past a relatively unexplored area of fish keeping that has many implications including prevention of HLLE in marine fish. As well 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/ORP 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.
Unfortunately some aquarists in their writings or anecdotal forum comments fail to look at the research that has gone on the subject of Redox and stick to their old tired theories about Aquarium Chemistry and the affect of Redox thereon much the same way many continued to claim the "earth was flat" even when proven incorrect.
It is important to note, that just because many aquatic articles report only the importance of an oxidizing Redox, this does not make it 100% correct, science is not a vote!.
I read a recent article that is easily found in search that is admittedly well written dealing with Aquarium Redox, with a good explanation as to what Redox is and more, however this article still chooses to repeat much of the same tired old information about only the positives of the oxidative side of the Redox equation, missing the evidence that the reduction side is also VERY important to a healthy Aquarium Redox Balance (I noted that the sources this particular article sited were all more than 15 years old which may explain much of the out of date information).
The basics of Redox are really not that hard to understand and are easily applied; that is knowing that a high bio load can have a downward effect on a good Redox while water changes, additional mineralization, UV Sterilization and more can have positive effect on Redox.
More simply stated; you can have too much oxidation, as well you can have too much reduction. However based on my years of experience and feedback, most understand the undesirability of too much reduction (such as "too high" of a GH), but fail to understand the issues of too much oxidation which hopefully readers will now understand better
Many aquarium keepers, especially advanced, are already applying many of the "best methods" for healthy aquarium redox without even knowing it.
Finally; maintaining a Redox below +350 mV while applying methods that might both permanently and temporarily achieve a Redox (low numbers are temporary) of about +350 to +100 mV for marine or +300 to -200 mV for freshwater are the raw numbers we are aiming for. (as per the graph in the background section).
For further information about WHY YOU SHOULD USE A UV STERILIZER
Another good article about this subject that I found is this: ORP and the Reef Aquarium
Here is a quote from the above article; “Many aquarists have been lead to believe that ORP is a measure of water quality or purity. Manufacturers selling ozonizers and other oxidizers (like permanganate) have been especially keen to present that idea.
This statement is where many aquarists have gone wrong in my opinion, A positive Redox is NOT a measure of water quality, but at least a Reducing Redox has more potential for a healthy aquarium.
*Redox and Electrochemistry
Please click on the "Buy Now" Button below for a pdf format downloadable e-book (23 pages) of this article as of 12/24/14 for $3.99 usd
PLEASE NOTE; You MUST click on "Return to American Aquarium Products" at the end of the transaction to be redirected to your download/e-book
For more aquarium information and articles (pond too):
If you have found this site helpful (or the sister site Aquarium and Pond Answers), please consider a donation to help with the 100s of hours of research and regular updates that go into these articles:
| Basic_Aquarium_Principles | Basic_Saltwater | Aquarium_Disease | Aquarium_Lighting | Goldfish_disease | Aquarium_cleaning | Nitrogen_Cycle | Redox_Potential | Clear-Pond | Aquarium_Filtration | Aquarium_Medication | Aquarium UV Sterilization | Vibrio_Aeromonas | Aquarium_Ich | Columnaris | Aquarium-KH | sponge_filtration | Aquarium-Plants | Quality_Fish_Food | Oodinium |
| Return Home | Aquarium_Information | Aquarium Products | Downloads | FAQ | Other | Contact Us | View Cart |