Relationship Between H2O2 & Redox (ORP) . . . Help with Explanation?

[esther]

Here's the deal... Having a little algae problem so I decided to dose H2O2. Have been watching how it affects the ORP value and it's fascinating to me. Would love some help trying to understand it. Seems like the adding of H2O2 daily is slowly increasing ORP. Once ORP gets to around 400mv, I'm going to stop dosing and see what happens. Can anyone explain to me what's going on? Thanks in advance!

Decided to dose 20ml of H2O2 every evening. Here's what the week looked like:

	Redox Before Dose	Redox After Dose
Day 1	225mv	99mv
Day 2	259mv	221mv
Day 3	272mv	225mv
Day 4	276mv	228mv
Day 5	299mv	228mv
Day 6	309mv	229mv
Day 7	317mv	223mv
Day 8	330mv	219mv
Current Measurement	341mv

 

[esther]

Anyone?

 

[Nano sapiens]

How about this...

Oxidation-reduction potential (ORP) or redox is a measurement that indicates how oxidizing or reducing a liquid is. You've added hydrogen peroxide, which is an oxidizer, so the ORP level went up

 

[Randy Holmes-Farley]

It has always confused me why ORP instantly drops when adding H2O2, which is an oxidizer.

My only theory is the it kills cells (e.g., bacteria) locally where added, and they spill their low ORP contents into the water.

As to why it is slowly rising, the fact that it is an oxidizer, noted above, would explain it. Or it might be unrelated drift.

 

[Nano sapiens]

It has always confused me why ORP instantly drops when adding H2O2, which is an oxidizer.

I had just quickly read the OP's text about ORP rising, but looking at the chart I can see that ORP initially dropped substantially when H2O2 dosing was initiated. Very interesting and not something that I would have expected!

 

[Randy Holmes-Farley]

I had just quickly read the OP's text about ORP rising, but looking at the chart I can see that ORP initially dropped substantially when H2O2 dosing was initiated. Very interesting and not something that I would have expected!

Me either, but it seems everyone sees that initial drop. I initially thought it might be use to other additives int he peroxide, and that may still be true, but it is hard to explain in detail.

 

[taricha]

This drop seems normal. It is a pH effect, otherwise, it should go up.

https://aquariustech.com.au/wp-content/uploads/bsk-pdf-manager/ORP_Chlorine_peroxyacetic_10.pdf

“Note that the dissociation constant (pKa) of hydrogen peroxide is 11.62, and hypochlorous acid (HOCL) is 7.4, expressed in terms of pH. It then becomes obvious that the peak activity of the Eo for hypochlorous acid is very near the pH of the water being treated, and the H2O2 is considerably higher. Thus, H2O2 would express a much lower ORP value at pH 7.4 than would hypochlorous due to the vast difference in the pKa constant.”

From Researchgate

“Simon - did you find the answer to this question? I have experienced the same result but I can't find a good explanation for the cause. My test conditions are 0.5M NaCl at 65°C. I injected H2O2 to produce 3 ppm H2O2 in solution and found that the potential dropped by about 150 mV”

 

[Dan_P]

Thanks for posting.

We should all just unplug our ORP probes. They are a totally useless diagnostic tool. Monitoring the oxygen level of the water would seem to make more sense if you are really interested in the health of your aquarium.

 

[Gordonm]

Well that ranked right up there.

 

[Randy Holmes-Farley]

There is no pH effect causing an ORP change here.

I do not understand what you are saying. Hydrogen peroxide (if pure) will not alter the pH of seawater it is in or added to. The pKa that is noted is above 11. Might be a bit lower in seawater, but it is not going to appreciably deprotonate at pH 8, and if it did, that would serve to lower pH which would raise ORP.

 

[Randy Holmes-Farley]

There is no pH effect causing an ORP change here.

I do not understand what you are saying, taricha. Hydrogen peroxide (if pure) will not alter the pH of seawater it is in or added to. The pKa that is noted is above 11. Might be a bit lower in seawater, but it is not going to appreciably deprotonate at pH 8, and if it did, that would serve to lower pH which would raise ORP.

 

[taricha]

There is no pH effect causing an ORP change here.

I do not understand what you are saying, taricha.

Bummer. I was hoping someone could help that explanation make more sense.

For kicks I pulled two tank water samples and filtered one through a 0.22micron filter, so it ought to be basically free of cells.
I then added h2o2 at 1mL/10L to each. The ORP didn't change much - maybe up a smidge.
I then went 10x as much, 1mL/L of (normal 3%) h2o2, and ORP went up around ~30-40 in both samples. No difference in the samples and no drop for me. Does this immediate drop in ORP from peroxide addition only happen in-tank, and not with isolated tank water?
If so, this sounds consistent with the idea that the h2o2 is lysing cells on surfaces and they release reducing substances into the water.

@esther if you pulled out tank water in a clean container and dosed the same ratio of h2o2 to water, would you still measure an ORP drop?

 

[Dr. Dendrostein]

Here's the deal... Having a little algae problem so I decided to dose H2O2. Have been watching how it affects the ORP value and it's fascinating to me. Would love some help trying to understand it. Seems like the adding of H2O2 daily is slowly increasing ORP. Once ORP gets to around 400mv, I'm going to stop dosing and see what happens. Can anyone explain to me what's going on? Thanks in advance!

Decided to dose 20ml of H2O2 every evening. Here's what the week looked like:

	Redox Before Dose	Redox After Dose
Day 1	225mv	99mv
Day 2	259mv	221mv
Day 3	272mv	225mv
Day 4	276mv	228mv
Day 5	299mv	228mv
Day 6	309mv	229mv
Day 7	317mv	223mv
Day 8	330mv	219mv
Current Measurement	341mv

Here's my take on it, hopefully it doesn't go over anyone's head, everything organic has a negative and positive charge in them the atoms that make molecules are negative and positive , so when you add the oxidizer that you're using it's pretty much disrupt the harmony between negative and positive ions and the meter orp picks up on it and the reading is in numbers we understand. Higher the orp, the less organic matter that can affect water chemistry is diminish.

 

[Dan_P]

Bummer. I was hoping someone could help that explanation make more sense.

For kicks I pulled two tank water samples and filtered one through a 0.22micron filter, so it ought to be basically free of cells.
I then added h2o2 at 1mL/10L to each. The ORP didn't change much - maybe up a smidge.
I then went 10x as much, 1mL/L of (normal 3%) h2o2, and ORP went up around ~30-40 in both samples. No difference in the samples and no drop for me. Does this immediate drop in ORP from peroxide addition only happen in-tank, and not with isolated tank water?
If so, this sounds consistent with the idea that the h2o2 is lysing cells on surfaces and they release reducing substances into the water.

@esther if you pulled out tank water in a clean container and dosed the same ratio of h2o2 to water, would you still measure an ORP drop?

i think you will have to also measure the H2O2 concentration in this experiment to make the two conditions comparable.

In isolated aquarium water H2O2 is stable, but in an aquarium it is depleted in 1-2 hours. I have made this measurement in my system. It is repeatable. This is why I think adding H2O2 to an aquarium is a useless action.

The stability depends on whether the sample contains organisms with an enzyme that destroys H2O2. In tank water there isn’t much of it. I wonder if this reflects that most of the bacteria in an aquarium reside on surfaces or most catalase containing organisms are attached to the surface. You will likely find that most of the depletion of Si, Fe, O2, etc. occurs on surfaces, further indicating water and surfaces are two distinct environments.

The drop in ORP occurs in brine solution. As Randy pointed out in an earlier post, if the brine solution is sterile, the cell lysis explanation is dead. I have no idea whether the posted results were done in sterile sodium chloride. I think duplicating the brine experiment with and without sterilization with H2O2 measurement is the way to go, that is if you think ORP and H2O2 are important in aquarium keeping

 

[taricha]

I think duplicating the brine experiment with and without sterilization with H2O2 measurement is the way to go, that is if you think ORP and H2O2 are important in aquarium keeping

That's true. I'm just curious if this effect people routinely see with h2o2 lowering their ORP short term disappears if it's done to tank water pulled outside the system. Or maybe my ORP readings are flukey. Haven't used it much.

We should all just unplug our ORP probes. They are a totally useless diagnostic tool. Monitoring the oxygen level of the water would seem to make more sense if you are really interested in the health of your aquarium.

It's likely true that if these controllers (APEX etc) shipped with O2 sensors in place of ORP probes, more livestock would be alive today.
...on the other hand, maybe it's not crazy that the relative amounts of reduced vs oxidized metals is relevant to nuisance growth in a system?

 

[Randy Holmes-Farley]

Here's my take on it, hopefully it doesn't go over anyone's head, everything organic has a negative and positive charge in them the atoms that make molecules are negative and positive , so when you add the oxidizer that you're using it's pretty much disrupt the harmony between negative and positive ions and the meter orp picks up on it and the reading is in numbers we understand. Higher the orp, the less organic matter that can affect water chemistry is diminish.

Sorry, but that is not any sort of scientific, chemical, or viable explanation.

 

[Randy Holmes-Farley]

...on the other hand, maybe it's not crazy that the relative amounts of reduced vs oxidized metals is relevant to nuisance growth in a system?

I would very much like to see more experimentation along those lines.

 

[Dr. Dendrostein]

Sorry, but that is not any sort of scientific, chemical, or viable explanation.

What you talkin bout Willis? Heeee

 

[najer]

I know a bit, look at Sochting Oxydators, there is a page here on r2r, I wish I had stuck with my chemistry and biology exams, There is an initial release of oxygen (this is where my science gets sketchy) molecules that can grab another to be happy ever after and this lowers the orp, look at people that run sensors and can show you traces, if I didn't use slow release oxydators I would dose the required amount split over at least 10 times or more through the day.

 

[Randy Holmes-Farley]

I know a bit, look at Sochting Oxydators, there is a page here on r2r, I wish I had stuck with my chemistry and biology exams, There is an initial release of oxygen (this is where my science gets sketchy) molecules that can grab another to be happy ever after and this lowers the orp, look at people that run sensors and can show you traces, if I didn't use slow release oxydators I would dose the required amount split over at least 10 times or more through the day.

I am very familiar with chemistry and ORP, and there is no simple chemistry explanation of how adding an oxidizer lowers ORP.