# Redox Paradox!



## DaveK (Jul 10, 2010)

The SW hobby went through a time where redox and ozone were quite the "in thing". While it's still used by some, it's not the be all, end all thing it was once considered. I found the article good, but IMO it's not worth worrying about redox, and related items such as ozone, unless you have a very specific issue to resolve that can not be solved by other means such as water changes.

If you are going to consider ozone, keep in mind that this can be an expensive investment. Also, it must be used safely. See this article (offsite) - http://reefkeeping.com/issues/2006-04/rhf/index.php

Having used both UV and ozone, again in SW systems, I'd say that ozone does a lot more than UV as far as raising redox and keeping water clear, removing tannins and so on. 

Perhaps the best question is, what is the issue your trying to solve? Ozone or UV might be a solution, but often you can get results without the investment in additional equipment.


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## Mxx (Dec 29, 2010)

It's not a single issue or goal. I wish to attain optimal water chemistry for the fish and plants. Lessening the need for water changes, or at least ensuring that water quality does not decline between water changes is something I'd certainly like to achieve as well as my time too is finite. And I don't want to be naive about my tank's ecology and water parameters and just follow practices blindly, so I do want to understand these things as thoroughly as I can. 

I appreciate there had been an ozone bandwagon which a lot of people jumped on until they apparently got distracted by something else, but that doesn't demonstrate whether or not it was a good idea. 

I was opposed to the idea of UV sterilizers as being unnecessary generally until I found they actually do impact the redox, and seem easier to use in any case than ozone. If they're not that effective at raising redox then perhaps they're not worth it in comparison. But if either does have a significant impact in terms of ensuring high water quality is maintained even as a precautionary measure then I'd prefer to use one for my next project.


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## Steve001 (Feb 26, 2011)

Mxx said:


> It's not a single issue or goal. I wish to attain optimal water chemistry for the fish and plants. Lessening the need for water changes, or at least ensuring that water quality does not decline between water changes is something I'd certainly like to achieve as well as my time too is finite. And I don't want to be naive about my tank's ecology and water parameters and just follow practices blindly, so I do want to understand these things as thoroughly as I can.
> 
> I appreciate there had been an ozone bandwagon which a lot of people jumped on until they apparently got distracted by something else, but that doesn't demonstrate whether or not it was a good idea.
> 
> I was opposed to the idea of UV sterilizers as being unnecessary generally until I found they actually do impact the redox, and seem easier to use in any case than ozone. If they're not that effective at raising redox then perhaps they're not worth it in comparison. But if either does have a significant impact in terms of ensuring high water quality is maintained even as a precautionary measure then I'd prefer to use one for my next project.


I agree we shouldn't follow practices blindly. And I found it odd that there's virtually no mention of redox potential on this forum. 

What we do is for some just a hobby, but it shouldn't be because what we are really doing with planted tanks is underwater horticulture and just like terrestrial horticulture it should not be a guessing game. I found another article on the subject. It's more current. 
*REDOX (REDOX POTENTIAL) BASICS (OXIDATION POTENTIAL, ORP):*

http://www.americanaquariumproducts.com/Redox_Potential.html


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## Mxx (Dec 29, 2010)

Steve001 said:


> I agree we shouldn't follow practices blindly. And I found it odd that there's virtually no mention of redox potential on this forum.
> 
> What we do is for some just a hobby, but it shouldn't be because what we are really doing with planted tanks is underwater horticulture and just like terrestrial horticulture it should not be a guessing game. I found another article on the subject. It's more current.
> *REDOX (REDOX POTENTIAL) BASICS (OXIDATION POTENTIAL, ORP):*
> ...


Was there supposed to be another link there to another article which didn't work? The only link was to the same main article I was talking about at the beginning. 

That was the article that talked in some detail about the ionization and magnetization of water, which was what had been dismissed by others as quackery. It all leaves you a little unsure about exactly what we should be believing though. 

If redox is that fundamental a parameter then I'm a bit annoyed that I hadn't heard about it before in any detail, so agreed that it's odd if it has so little mention. But it means I should make some modifications to my practices including increasing oxygenation via surface turbulence, and indicates that perhaps I may have not ideal levels of redox considering my ratios of flora/fauna bio-density. 

But more to the point, is Redox the supposed mysterious reason to actually do water changes? (In case that other parameters such as nitrates were low and in case we're not doing EI)?


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## Jeffww (Aug 6, 2010)

If you're that obsessed with water quality build a foam fractionator (giant FW skimmer basically) and save yourself some headache and risk.


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## Hoppy (Dec 24, 2005)

It's a hobby! So, you "should" do whatever enhances your enjoyment of the hobby. If that includes playing with/measuring/ using REDOX by all means do so. If you just want an attractive healthy planted tank, it isn't necessary to even know what REDOX stands for. All I ask is that you share your knowledge, and findings with us, to enhance our enjoyment of the hobby.


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## Steve001 (Feb 26, 2011)

Mxx said:


> Was there supposed to be another link there to another article which didn't work? The only link was to the same main article I was talking about at the beginning.
> 
> That was the article that talked in some detail about the ionization and magnetization of water, which was what had been dismissed by others as quackery. It all leaves you a little unsure about exactly what we should be believing though.
> 
> ...


My mistake with the link. Ignore it.


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## Mxx (Dec 29, 2010)

Hoppy said:


> It's a hobby! So, you "should" do whatever enhances your enjoyment of the hobby. If that includes playing with/measuring/ using REDOX by all means do so. If you just want an attractive healthy planted tank, it isn't necessary to even know what REDOX stands for. All I ask is that you share your knowledge, and findings with us, to enhance our enjoyment of the hobby.


Fish are happy, I'm happy. Fish get a disease, fishkeeping's then not so fun. 

Hoppy, in researching this topic I also came across your RFUG with CO2 thread from a few years back, which was quite interesting for me as I was just considering trying some similar things. Do you think there is any way to do that in combination with using MTS though? I really do want to try the idea of CO2 in the substrate, even if I happen to have very minimal water flow through it or maybe just a recirculating loop that I'm bubbling CO2 into. I'm not sure how to do that in combination with soil though, maybe covering the piping with a sheet of foam first, which the CO2 could bubble into and be held by or something. (How is that for hijacking my own thread!).


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## Hoppy (Dec 24, 2005)

Mxx said:


> Fish are happy, I'm happy. Fish get a disease, fishkeeping's then not so fun.
> 
> Hoppy, in researching this topic I also came across your RFUG with CO2 thread from a few years back, which was quite interesting for me as I was just considering trying some similar things. Do you think there is any way to do that in combination with using MTS though? I really do want to try the idea of CO2 in the substrate, even if I happen to have very minimal water flow through it or maybe just a recirculating loop that I'm bubbling CO2 into. I'm not sure how to do that in combination with soil though, maybe covering the piping with a sheet of foam first, which the CO2 could bubble into and be held by or something. (How is that for hijacking my own thread!).


I don't think it will be possible to use a RFUG with MTS or any fertile substrate. But, you could isolate one section of substrate in a large tank, and have a RFUG there. One of our regulars in India uses that method for filtering, except just a regular undergravel filter - isolated to a small area of the substrate. If the substrate is loaded with nutrients, circulating water up through that substrate might overload the water with the nutrients.


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## plantbrain (Dec 15, 2003)

I did RFUG 20 years.............

Redox should be quite high in any FW tank, about 400.

Few bother with it.

It's a sediment parameter.

DO(dissolved oxygen) is better for FW if you want to monitor some parameter related to the health of the plants/fish. :icon_idea
You like wild goose chases, go after a few of them Canadians please.


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## Steve001 (Feb 26, 2011)

Mxx said:


> Fish are happy, I'm happy. Fish get a disease, fishkeeping's then not so fun.
> 
> Hoppy, in researching this topic I also came across your RFUG with CO2 thread from a few years back, which was quite interesting for me as I was just considering trying some similar things. Do you think there is any way to do that in combination with using MTS though? I really do want to try the idea of CO2 in the substrate, even if I happen to have very minimal water flow through it or maybe just a recirculating loop that I'm bubbling CO2 into. I'm not sure how to do that in combination with soil though, maybe covering the piping with a sheet of foam first, which the CO2 could bubble into and be held by or something. (How is that for hijacking my own thread!).


Vascular aquatic plants have a process called _guttation_. This creates a very slow flow through the substrate.


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## Mxx (Dec 29, 2010)

Okay, so whether it's DO or Redox, and regardless of whether we measure it even, the principle remains the same that for the health of our fish it is important that we should plan our systems to aim for relatively high values, right? 

And that a UV sterilizer will help with that, with an ozonizer helping even more, correct?

Apart from that, how much stock should I generally put in the Redox article by Mr. Carl Strohmeyer?

In terms of the RFUG it's simplyabout creating a CO2 rich plenum under the plants, not to utilize it for filtration or flow (which I'd aim to keep very minimal actually), though there are questions about whether CO2 there would work for the plants.


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## Hoppy (Dec 24, 2005)

The easiest way to keep a high level of dissolved oxygen in the water is to maintain good water surface ripple over the whole water surface. When I used my RFUG I hoped to get better distribution of CO2, and by doing that, get less BBA. It didn't make any difference in that regards, as far as I could see. But, the water clarity was outstanding. Most of my filtering then was done with a canister filter, with it's output going to the RFUG.


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## Mxx (Dec 29, 2010)

Trying to draw some conclusions now, it seems that Redox is a combination of different factors - organic pollutants in the tank/oxgen levels/calcium and magnesium levels/etc. So similar to how ph which is a affected by various factors including minerals/acids/CO2 in the tank, Redox isn't an exact science or an altogether clear thing to measure. And perhaps it is rather a crude indicator of organic pollutant levels, but somewhat an indicator nonetheless. But even if we don't know or need to know specific Redox levels, that doesn't mean we can't do things to raise the Redox.

Thus, in terms of removing those organic pollutants indicated by low Redox levels, we can generally handle those either of two ways in case our plants aren't doing it sufficiently. We can do do either water changes, or we can use ozone/UV sterilization, but both manage to equally accomplish the same thing in terms or lowering organic pollutant levels and thus raising Redox, is that correct?


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## 58417 (Dec 18, 2012)

I would like to resurrect this thread with the following paradox:
I have a very small tank (3G = 12L) with lava stones and akadama as a substrate. I put there (into the substrate) a really big amount of fertilizer for terrestrial plants also, so after I filled it with water I had more then 150 mg/L NO3 (confirmed laboratory analysis). Also I use LED light with more then 100 µmol PAR at the substrate level (and around 150 µmol PAR at water surface). All the tank is full of algae, which is no surprise under these circumstances. But, what surprises me a lot are two things:
1) COD is very low (<0,5 mgO2/L)
2) ORP is extremely high (+510 mV, and each day keeps increasing!)
According to what I have read concerning algae and ORP (redox), in the tanks where there are algae problems, the organics should be high, and ORP should be low ... but that's not the case with my tank.
*
Is there anybody who can explain this to me?*

According to this post: barrreport.com, such a high values as I have should be dangerous for fish, so how can that be that in my tank the ORP is so high, although I do not add anything in there (except a small doses of liquid carbon, as I don't use pressurized CO2 there). I don't use any fertilizers, and I have only a very small HOB filter there.

PS: The tank is about 2 months old. You can look at it here: www.prirodni-akvarium.cz (test #3).


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## JoeRoun (Dec 21, 2009)

*Just Tryin' to Make a Living-Times Are Tough...*

Hi Marcel,

In as much as you have 150-mg/l (ppm) Nitrates and are not fertilizing that means that ammonia/ammonium is coming from somewhere.

I am sure the terrestrial fertilizers are producing the ammonia/ammonium, beyond what the algae can consume and your biological filtration in this case just happens to include algae and will continue to do so until the excess nutrients are consumed (exported). 

You are providing a lot of light and no creatures to add organic material to the water so it is extremely clean. Getting close to a level that could harm the critters keeping it so clean.

More later, I have some real life issues I am dealing with at the moment.

Respectfully,
Joe
FBTB


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## 58417 (Dec 18, 2012)

Hi Joe,

yes, the source of such a high nitrates is for sure the terrestrial fertilizer which is leaking through the substrate into the water column. I can fix that, but I would like to test this unusual environment, so I just let it be ... not doing anything with it for now. As there are no critters I need not worry. There are just some indestructible snails.

I was just curious why could it be that I have such a high ORP in there + a lot of algae at the same time ... because according to the table on barrreport.com at such a high ORP the environment should be algae-unfriendly.

Marcel


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## JoeRoun (Dec 21, 2009)

*Cycles*

Hi Marcel,

Yes, with the ORP values climbing into the 500-mV ranges for sustained periods of time, the water is becoming an increasingly hostile environment for the microbes, what you have is nature’s version of added hydrogen peroxide. These really is no paradox, your system is working hard to find equilibrium.

You have a young system with a tremendous amount of added energy (lights mainly), extreme nutrient load, nowhere near enough plants to consume/export the nutrients.

I would say it also makes me think the tank temperature and pH are likely (relatively) low.

Best guess is the HOB filter is “slimy,” a good load of biofilm, this is the protection for the microbes from the oxidizer. I would assume the same would be true at the substrate surface. The lava rock provides an excellent environment for the nitrifying bacteria. The algae is consuming a great deal of nutrients and producing a good deal of oxygen, in fact, producing hydrogen peroxide.

I am assuming COD test with potassium dichromate (best) or potassium permanganate (okay) with the excess oxygen estimated by titration.

The problem with COD (chemical oxygen demand) as an indicator in this case is the high oxidation level of the solution, would seem to be an interference.

I like that you are allowing this to proceed, I have done this a couple of times but at half (or less) the light you are using. In each case, the tanks went through a “crash,” then recovered and went on to be stable systems.

Our aquariums do not really cycle, s in the neat way the advertisers would have us think; there are several cycles, really, it is closer to waves. In systems not reasonably balanced, they simply have a more dramatic way of achieving equilibrium.

Respectfully,
Joe
FBTB


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## 58417 (Dec 18, 2012)

Hi Joe,

the temperature is somewhere around 22°C (72°F), so it's low. The pH is ~5.4, so also very low. I know this environment is not good for microbes. In normal case I won't allow the tank to have such a hostile conditions too long. Normally I do my best to up the temperature and pH, and have a reasonable level of oxygen for microbes to work effectively, so that the tank can stabilize as soon as possible. But as I already said, I did not understand the high ORP values. You say that the reason is probably algae producing hydrogen peroxide. I have to say I did not know that algae can produce H2O2, but that would explain a lot.

*Still, that lead me to another question:*
_Why I do not have such a high ORP values in my second tank, where there is even stronger light (around 120 µmol PAR at the substrate), and much more plants? I have another 15G tank with quite efficient canister filtration, CO2 supply, ADA Aqua Soil substrate, only 10 little sakura shrimps ... where the ORP is between +350 to +400 mV. There are virtually no visible algae. But why the redox do not go as high as in the small 3G tank? Do you think that algae produce more H2O2 then plants (if both has about the same biomass)? Or does filtration or water movement "outgass" the H2O2 (as in the bigger tank I use better filtration and ripple the water surface, unlike the smaller one)? Or do I "reset" the ORP each time I change water in the bigger tank ... so if I stop doing water changes, the ORP will finally come to similar values as in the smaller tank (where I don't do water changes as often)?
_
Thank you, Joe, for your comments.

Marcel


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## ChemGuyEthan (Apr 13, 2014)

I'll weigh in here a little, too. First I must say that the article posted in the original post of this thread is hard to believe. The author has several misconceptions of basic chemistry that lead me to question the rest of his theory on maintaining an overall neutral ORP. I think in the end the well maintained tank will establish itself and the ORP will not need be monitored unless something disturbs that equilibrium value.

I can understand how an oxidizing environment is more beneficial than a reducing one. I mean, we are living in an oxidizing environment with molecular oxygen all around us. I would assume the small microorganisms like bacteria and algae are less capable (in general) to survive in more oxidizing environments than complex animals and plants. 

Joe's comment on algae producing peroxide intrigued me, so I looked into it a bit. It seems that some types of cyanobacteria (may be others too) will produce H2O2, but not all. And plants may produce it when stressed, but I don't believe the production rate is high. I saw in your post you listed cyanobacteria as present in this tank, so perhaps they are the culprits of the ever-increasing oxidation potential.

I must also agree with Joe on the new tank and say that I doubt many studies have been done on the resting potential of new tanks so I would believe little is known about what sorts of changes occur as the plants, bacteria, and other organisms establish themselves in the new environment.

H2O2 cannot be "out-gassed" as it is not a gas. It does break down fairly quickly in bright light when dissolved in water, this would produce mostly molecular oxygen and water, but also some radical species (further leading to a higher oxidation potential). I would think a water change should be decreasing this potential as you are removing the species in the water making giving the higher ORP measurement. 

I think that's the basic theory behind monitoring this value at all. You're keeping track of the accumulation of oxidizing species in the aquarium to know when a water change is necessary. Or maybe that's what it started out as. I would be willing to bet that under normal tank conditions (well established tank, regular water changes, healthy plants and animals) the ORP value is probably fairly consistent and well within tolerable ranges.


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## plantbrain (Dec 15, 2003)

kwisatz said:


> Hi Joe,
> 
> the temperature is somewhere around 22°C (72°F), so it's low. The pH is ~5.4, so also very low. I know this environment is not good for microbes. In normal case I won't allow the tank to have such a hostile conditions too long. Normally I do my best to up the temperature and pH, and have a reasonable level of oxygen for microbes to work effectively, so that the tank can stabilize as soon as possible. But as I already said, I did not understand the high ORP values. You say that the reason is probably algae producing hydrogen peroxide. I have to say I did not know that algae can produce H2O2, but that would explain a lot.
> 
> ...



Low pH due to CO2 enrichment vs low alkalinity or acids are two different things. My pH's sit about 5.7, no issues with NH4 and NO3 drops to zero after 3-4 days after dosing 15 ppm as KNO3, this includes a well fed fish stock at well over 2 inches per gallon. I do not have skinny fish. Ask Joe above who's been to my house recently. 

Reduction= good for the sediment within a range(N and Fe reduction), oxidation everywhere else=good. 

Small tanks and lots of light, rich sediments, well....not the best place to do a test, larger tanks seem to modulate the effects better, are more stable and the filtering seems much less sensitive. Light spread from say 45cm vs 5 cm is also very different. 

I would not over look such differences.

Frequent water changes, this will help most any tank(particularly new ones), and should increase the Redox values. 

Seems that many folks do not take the 2-3x a week water change routine serious for the new tank set ups, this is unfortunate. I know several top folks with decades of experience and we all seem to have the same advice there. 

There is some correlation, but is the key Redox? I'm doubtful frankly.
Redox is mostly used for aquatic plant research for sediment, no one really uses it for the water column. O2 yes, but not redox. I'm not clear on the justification, but good O2 is telling for most water column parameters.

Bump:


ChemGuyEthan said:


> I'll weigh in here a little, too. First I must say that the article posted in the original post of this thread is hard to believe. The author has several misconceptions of basic chemistry that lead me to question the rest of his theory on maintaining an overall neutral ORP. I think in the end the well maintained tank will establish itself and the ORP will not need be monitored unless something disturbs that equilibrium value.
> 
> I can understand how an oxidizing environment is more beneficial than a reducing one. I mean, we are living in an oxidizing environment with molecular oxygen all around us. I would assume the small microorganisms like bacteria and algae are less capable (in general) to survive in more oxidizing environments than complex animals and plants.
> 
> ...


Well, if the CO2 was off suddenly, you would see some Redox changes, and the O2 levels would fall, the DOC's should build up as well, surface scum increases, poor plant growth, growth stops, fish are more active suddenly, less pearling, there are *many* signs.

O2 would be perhaps a better paramater, but more costly to monitor.


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## JoeRoun (Dec 21, 2009)

*Assume: Ass of U & ME*

Hi All,

Apologies first, I certainly misstated on hydrogen peroxide; I think I meant to say “hydrogen peroxide-like,” based on the addition of all the oxygen. I think I was trying to say what ChemGuyEthan said.

I am in agreement with Tom’s assessment.

I also failed to clarify and made assumptions about Marcel’s tank that were obviously incorrect. My bad.

When I said, “the tank temperature and pH are likely (relatively) low” I was not thinking pH 5.4 low. The fact is that my assumptions about nitrifying bacteria would be incorrect, as they would not be in significant numbers at pH 5.4 generally and especially not in high ORP value water. In other words not much slimy stuff.

The other part of this is the numbers referenced by that low-life Biollante, are based on Chris Walster’s article in the “Summer 1997, Koi Health Quarterly.” Though I have not checked my guess is that that no-goodnick Biollante, adjusted the values for warmer water (as the evil plant monster is involved mainly with tropical plants), and likely the whole thing is based on pH in the pH 6.8-7.8 range.

Another point in my email was that since the Nitrate levels Marcel cited are likely from chemical (I think he meant to say, “salts”) rather than organic material and the system has not had time to create its own wastes the COD reading is likely correct.

The good news is that at pH 5.4 and 22.2C (72F) there is virtually no ammonia.

I also admit that had this been anyone other than Marcel, I probably would not have answered in a thread so obviously based on the Carl Strohmeyer religious tract. I do not care to get involved in religious arguments.

I will give this much were Marcel to chop up a little bit of a vitamin C tablet and add it to the water it would bring the ORP values down, in as much as it is an antioxidant.

Respectfully,
Joe
FBTB


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## 58417 (Dec 18, 2012)

Hi all,

first of all, thank you for your comments!

Unfortunately, my concern is *not to remedy* the current situation in my tank (if the tank collapses totally I won't regret), *but to understand *why the redox in there is at such a high levels (today my calibrated "Extech SDL100 pH/ORP Meter" is reading +540 mV!). When I add microelements the ORP drops for a while (due to organic chelates?) ... but after a while it returns to 500+ values and keeps increasing each day. *What the hell is going on in there? *I would not believe that the plants inside produce that much oxygen, because the only pearling species are some algae under the water surface. Also, as I said already, I have another tank where there are much more plants, most of them pearling under strong light, but the ORP values are much lower compared to the first tank (only +350 to +400 mV). But it's true that even in this second tank the *ORP is slowly increasing*, so maybe if I stop doing regular water changes each week in the second tank the ORP will also increase to such a high values. But as I have shrimps in there I just don't want to try/risk it. BTW, as my tap water has ORP of about +200 mV, the water change definitely decreases my ORP (not increasing). But right after the water change it keeps increasing.

Unfortunately I don't have any meter for measuring dissolved oxygen levels (I'll have one but it arrives until after 4 weeks). Also the *cyanobacteria *are no longer in this tank (at least I do not see them), the same apply for most of *green algae *(they too just disintegrated). The only algae remaining inside this tank are *diatoms*. Plants (anubias + alternanthera reinickii mini) are not doing well ... they're loosing color (probably due to low microelements or potassium as the venation in anubias leaves is yellow?). Also the nitrates are a bit now lower. As I said, I want to understand what is actually responsible for increasing the ORP so much. It seems more logical to me that the reason for such a high ORP values have something to do rather with some radical species then molecular oxygen itself. But I can be wrong. *What do you think?*

Marcel


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## JoeRoun (Dec 21, 2009)

*I Am Not Sure I Understand*

Hi Marcel,

You are adding information as we go, but I believe it is consistent. 

I understand you are not and were not looking for a remedy, however in explaining what is happening I am giving you the reasons in terms of the system (your tank). Among the reasons, we do the things for tanks, filtration, water changes, so on, especially early in the life if the system is to avoid these extremes. Your system as with everything in life are seeking equilibrium.

I think the chart you referenced was designed a general guide and as far as I can tell, based on your reporting it seems that it is.

I am not sure I understand your apparent distress, increasing ORP values are doing exactly what we would expect, the cyanobacteria are gone, much of the microbial life as well no doubt, the algae is beginning to fragment, die, the macrophytes are starting to deteriorate. What precisely is not happening in accordance with the ORP chart you referenced?

The ORP values may be a little different, perhaps due to temperature and pH, but everything is within the range.

Yes, I believe the ORP values decline as a result of materials you add, I am unclear what you are adding but yes things we add can increase or decrease ORP values.

As I said earlier, I believe the ORP values will continue to rise until enough organic material is produced to “use up” the oxidizing potential created. The numbers you are reporting are consistent with the use of potassium permanganate, ozone or hydrogen peroxide.

This is not to criticize just being sure I understand ORP values temperature sensitive and are often pH dependent, ORP readings take time (20-minutes), ORP probes can only be reliably calibrated to one value.

In some ways, this has the feel of an ambush. I am happy to go as far as my experience allows me, I do not profess to have all of the answers and ORP is complex so without knowing the variables I think the answers are in general terms. To be honest I see nothing surprising in your situation. It rather confirms the advice we tend to give beginners (what Tom said).

Respectfully,
Joe
FBTB


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## ChemGuyEthan (Apr 13, 2014)

plantbrain said:


> ...Frequent water changes, this will help most any tank(particularly new ones), and should increase the Redox values...
> 
> ...O2 would be perhaps a better paramater, but more costly to monitor...



Tom, I'm not sure I understand why a water change will raise the ORP? Related to dissolved oxygen? Would you elaborate on that? I guess it would also depend on the potential of the water you're adding to the tank so in that case it's a relative statement. But as this value is simply a bulk measurement on the species in solution, removal of the oxidizing species and replacement with neutral, less oxidizing, or even reducing species can only result in a lowering of the bulk potential.

I agree O2 is a much better estimate of the health of the system as it pertains not only to the surface agitation, but also the plants CO2 consumption/O2 production, and the healthy respiration of the fish. I'm not advocating trying to monitor this ORP parameter that closely as I just learned about it today by reading through this thread, haha. But as a chemist, I have more than a basic understanding of electrochemistry and am trying to figure out how much of that knowledge will translate over to this topic. 

Do we really know exactly what species give rise to a higher oxidation potential? I can imagine ions like iron being oxidized from ferrous to ferric giving an overall more oxidized potential, but that doesn't mean those ions are necessarily harmful. Others I can think of are of course oxygen, but also copper (cupric form), and nitrates. And the existence of persistent radicals in solution seems unlikely to me as the metal ions that are also in solution are capable of quenching those radicals and being reduced.

Anyway, I think ORP is kind of a silly measurement for the aforementioned reasons. As it is a bulk measurement, there are so many factors that can go into raising the resting potential of the system that it will be impossible to pinpoint exactly what's causing the extreme value. It may not be that an inherent high value is damaging to the system, but a specific species contributing to the oxidizing potential is the harmful component. 

Whew...anyway, sorry for the monologue. This topic has piqued my interest regardless of how much stock I put into the significance of the measurement.



kwisatz said:


> Hi all,
> 
> first of all, thank you for your comments!
> 
> ...


I guess the only thing I will submit in response to this is that the microelements mixture probably contains reduced metal ions, like ferrous ions. These will inherently lower the overall potential of the system and as they are slowly removed from the system (either by uptake from plants or by oxidation to the ferric state) the potential will rise again.

Also, do you work in a lab or something, Marcel? Or just have lots of excess money around to buy these instruments for measuring all these values? Haha


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## JoeRoun (Dec 21, 2009)

*Useful For Trends*

Hi Marcel, All,

I am someone who likes ORP as an indicator of water quality; I do not believe ORP has much value as a target. 

An ORP value gives me a good idea of aquarium water quality as long as I understand the rules of the aquarium; from there I can help, maybe.

I admit that years ago Tom, Plantbrain, told me this would be the problem with using oxidation potential for monitoring aquarium water quality. There are too many variables and the desire to use ORP values as a sole determinate. It is fine for pools or waste treatment with agreed upon rules and ranges, but for aquariums... Oh well...


Respectfully,
Joe
FBTB


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## 58417 (Dec 18, 2012)

*Science vs. religion*



ChemGuyEthan said:


> Also, do you work in a lab or something, Marcel? Or just have lots of excess money around to buy these instruments for measuring all these values? Haha


Actually, I'm quite sure I have a lot less money than most people around, but I have a very strong desire/need to understand things going on in my tanks, so that's the reason I put all my spare money into this hobby to understand it better (as so many people only talk about it, but not test it). No one else seems to do it for me. Tom share a lot of things from his own findings, but no solid data (just conclusions). Probably, one day I arrive at the same conclusions but meanwhile I need some data to make me believe.


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## 58417 (Dec 18, 2012)

*Attempt to explain my motivation*

Joe, I really respect you, and value your opinions.

I understand that my system is seeking equilibrium. Also I understand that ORP is a kind of bulk measurement, and we don't know what species predominate in the solution, so we can not be sure if there is just higher level of harmless oxygen, or some dangerous radicals etc.

My problem and reason why I asked my questions, was based maybe on a wrong assumption, that "in any tank the reduction processes prevail," so if we don't do anything finally our tank will enter a state of *dung-water with very low redox* (= accumulation of organics, lot of algae, bad water quality etc.).

But now (from what you said, and from what I see in my tank) it seems that this is just not true, and that (at least) in my tank the oxidative processes prevail, so if I don't do anything, the system will finally enter a state of *germicidal disinfective solution with extremely high redox*. Do I understand it right?

Marcel


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## JoeRoun (Dec 21, 2009)

*All the Varibles, One Kid A Brain Surgeon the Other an Addict*

Hi Marcel,

You are seeing one possible outcome, I have seen similar outcomes at least twice (while paying attention anyway); I am not experienced or educated enough to give you definitive reasons. All I can offer are best guesses, sometimes these things just seem to take tracks of their own, the reason I suppose when experimenting it is important to set up dozens of tests so that with a statistical analysis we can come to some conclusion.

In the case of your tank, I have no idea what was in the “terrestrial fertilizer,” you added in the beginning, when people use that term I generally think high ammonium, as I did in my original answer. Obviously, there are other constituents and unlike the United States, I know that some countries mandate other additives, by region to improve the soil. For all I know there is an oxidizer included in that “terrestrial fertilizer.”

Remember things such as Cobalt, Aluminum and Chlorine, followed closely by Oxygen and Bromine, with copper bringing up the rear are major oxidizers. 

You dismiss Oxygen, okay, I do not know beyond what you tell me is in your tank. You say you do not see any “pearling,” is there any consideration the Oxygen could be doing something other than bubbling away? You say you see “pearling from the substrate, have you tested the gas?

All I am saying is that the chart you are citing appears to be roughly correct.

I guess the best answer to your question “Do I understand it right?” regarding the two statements 


1) “if we don't do anything finally our tank will enter a state of dung-water with very low redox (= accumulation of organics, lot of algae, bad water quality etc.).” and 


2) “if I don't do anything, the system will finally enter a state of germicidal disinfective solution with extremely high redox,” 
The answer is yes.

Unless something else happens. I could imagine another outcome where the oxidizing material is used up and the system balances itself without a crash.

Sometimes all we have are sets of possibilities and based on our experience we give our conclusions, or in my case “best guess.”

Respectfully,
Joe
FBTB


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## brandon429 (Mar 29, 2003)

ChemguyE
I have a question about this

*It does break down fairly quickly in bright light when dissolved in water, this would produce mostly molecular oxygen and water, but also some radical species (further leading to a higher oxidation potential). *

We show a consistent lowering of orp when adding peroxide, at least in reefs, why is this? I know it goes against chem theory, there's something interacting in the tank but its really consistent on threads where peeps with orp eq show a lowering of it, not a raising

they had posted that organic interaction changes the nature of what h202 does in plain water? so I wonder at what point does peroxide actually sustain a rise in orp since the organic loading is pretty much endless in our tanks

Im assuming due to the nature of organic sinking this phenomena is probably worse in fw tanks that are getting dosed, meaning a total orp drop until breakdown of the molecule is complete. I like getting peroxide feedback where possible, and where it goes against what lots of posters have listed its even more interesting.


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## ChemGuyEthan (Apr 13, 2014)

kwisatz said:


> Joe, I really respect you, and value your opinions.
> 
> I understand that my system is seeking equilibrium. Also I understand that ORP is a kind of bulk measurement, and we don't know what species predominate in the solution, so we can not be sure if there is just higher level of harmless oxygen, or some dangerous radicals etc.
> 
> ...


Well you are doing something, with a filter you're adding oxygen to the system. And I agree with Joe, there may be other ions in the fertilizer you used that don't traditionally find there way into most people's aquariums, giving you abnormally large, positive potentials.

But I think in a normal system, if you leave it sit (think of a stagnant pool of water), it will have low dissolved oxygen, build-up of organic compounds from the decomposition of dead material, loss of reduced ions for flora consumption, all of this contributing to "the reductive processes prevailing."

You're system is ever-evolving, between the fertilizer, plant growth, and oxygen addition. I'm not sure you can translate what you're observing in this small sample size to the larger picture. And as frustrating as it may be, you might never know what it is exactly in your system that's giving you the high potentials and therefore not understand the process completely in this case. 

Designing an experimental setup would take more work like starting from a fresh, clean system (no ferts, inert substrate, fast growers probably) and slowly introducing "contaminants" (oxygen, CO2, NO3, NO2, NH3, CO3, PO4, H+, Ca2+, Mg2+, other trace metals, etc) one by one to determine which contribute to the potential change and then additional studies where multiple "contaminants" are introduced together to observe the cooperative effects of the system as it changes. Overall this would take hundreds of experiments/tanks to truly understand the dynamic ecosystem in our aquariums.

Now despite what I'm saying, I don't mean to belittle your experiments. I appreciate very much your enthusiasm and passion for understanding what's happening. My concern is too many variables.



JoeRoun said:


> Hi Marcel,
> 
> You are seeing one possible outcome, I have seen similar outcomes at least twice (while paying attention anyway); I am not experienced or educated enough to give you definitive reasons. All I can offer are best guesses, sometimes these things just seem to take tracks of their own, the reason I suppose when experimenting it is important to set up dozens of tests so that with a statistical analysis we can come to some conclusion.
> 
> ...


I agree with most of what you said Joe, expect your list of "oxidizers." Most of those in their elemental form are reductants (cobalt, aluminum, copper), and in their oxidized forms would be mostly inert in an aquarium environment (save for cobalt(3+), which may have more interplay with cobalt(2+)). And aside from oxygen, and maybe chlorine, I don't think any of those elements would exist in an aquarium. Their ions, sure, but not the elements. That's an important distinction that needs to be made when establishing their effect on the potential.


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## 58417 (Dec 18, 2012)

*Thanks for shedding light!*

The "terrestrial fertilizer" I used is called Cererit, which is a fertilizer without any chlorine (8% N, 13% P, 11% K, 2% Mg, 15% S + trace elements like B, Mb, Cu, Zn). This fertilizer is used in a couple of substrates for aquatic plants in our country, so it should be safe. But as I said, I used too much of it in my substrate (which was bad idea). The only other thing I was adding to this tank was liquid carbon (Easy-Life EasyCarbo) as a source of carbon for plants.

I don't dismiss oxygen as potential oxidizer which could be responsible for increasing the redox in my tank. I just thought that the amount plants are producing is not big enough for such a high values (+540 mV) ... that's all. And when I spoke about "pearling" I meant the same think = my assumption that when the plants are not pearling, they are not adding enough oxygen to increase the redox to such a high level. 

But now I see it from another perspective, so now it seems to me that if there is very small amount of organic sources in the tank, then even small addition of oxygen from plants and algae can lead to high redox ... if there are no counter-species (reducing ones) that can consume the oxidative species (thus lowering the redox). And you are of course right => when I abandon my wrong assumption (that in any tank the reduction processes prevail), than everything seems more clear now (even the very high ORP values). And of course, if some organics (or other reducing species) show up in my tank, then the oxidative species will be used up (at least to some extent) and the system balances itself.

Thank you very much for shedding some light on this problem.

Marcel


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## ChemGuyEthan (Apr 13, 2014)

brandon429 said:


> ChemguyE
> I have a question about this
> 
> *It does break down fairly quickly in bright light when dissolved in water, this would produce mostly molecular oxygen and water, but also some radical species (further leading to a higher oxidation potential). *
> ...


Hmmm, interesting. I guess I hadn't thought about that aspect of things, so that was neglect on my part, haha. I'm sure if you added a lot of peroxide it would raise the ORP quite high, but then people wouldn't have their pretty planted and reef tanks, haha. So assuming it's responsible dosing then the peroxide is there to chew up these built-up organic compounds. Now without knowing what these are, it's a little tough to say what might be going on, but I'll speculate away.

So if the organic compounds have an oxidizing potential of their own, reasonably high, but not outrageous, then upon addition of peroxide (which has a more outrageously high oxidizing potential) then they will react with one another. This reaction essentially quenches both oxidizing species resulting in an overall lowering of the ORP. The H2O2 is gone, probably generating water only, no oxygen or radicals, and the once mildly oxidizing organic compound has changed chemically and lowered the effective ORP. 

I think that makes sense to me, so it doesn't counter chemical theory, just chemical theory in pure water, which is not what we have here, haha.


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## brandon429 (Mar 29, 2003)

Nice. yes its true they are adding just baseline safe doses, nobody measured the overdoses and reported so that sounds reasonable. thanks for the input always good to read about the nature of h202 in any setting


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