Test if it is possible to explain the know ORP reduction when adding H2O2 into a saltwater

[taricha]

I am waiting to see what @taricha finds when he doses persulfate to a water sample.

Like hypochlorite and permanganate, persulfate increases the ORP of aquarium water in a repeated dose dependent manner (but less).
The effect from strongest ORP move to least is bleach > permanganate > persulfate.

Each of the first 3 humps is an addition of +5ppm sodium persulfate, the fourth hump is +10ppm.

It seems peroxide is unique in that it simply does not interact with the ORP probe itself, so we only detect it indirectly by what it does to other things.

 

[taricha]

I am thinking of joining you and @Hans-Werner on the biofilm/electrode conditioning effect.

My current thinking is that it's metals and the details get mediated by the biofilm/ probe effects.

I do wonder now if we need to change our investigation into finding a method to reproducibly condition a new or thoroughly cleaned ORP electrode so that it produces well defined dips?

This is my issue with the biofilm idea. It implies that there's some cleaning routine that could be done to a probe showing the drop with h2o2 that would turn off the effect.
Scrub + detergent for biofilms?
Acid to remove deposits?
Ethanol to dissolve other organics?

But no indication so far that cleaning a mature probe turns off the effect.

 

[Hans-Werner]

Scrub + detergent for biofilms?

My fingers where already itching when @Lasse wrote about his toothbrush, toothpaste mabe? Would this damage the electrodes? I mean, it is what we use with a toothbrush to clean or teeth from biofilms. Not totally serious.

 

[Lasse]

The problem with cleaning is that the external junction and the glass membrane both most be cleaned from biofilm. I do not know where they are situated on the prob. However toothbrush and alcohol should probably do the job. But in that case - can we differ a biological effect from an equilibrium effect?

Sincerely Lasse

 

[taricha]

But in that case - can we differ a biological effect from an equilibrium effect?

If cleaning turns off the effect, we can say which is more likely by the time it takes for the effect to return.
Min to a handful of hours - post-cleaning equilibrium.
Day to weeks - biofilm re-establishment.

 

[Rick Mathew]

Do you have a plot of the H2O2 ORP dip? If you scaled the plot to the size of your food addition dip, would they be a perfect match?

Actually they are much different...Have a look at the data below

Data from the Experiment: (From the charts I posted)

H2O2 add----Initial ORP 290
After add 262
Difference 28
Time to minimum Approx. 30 min
Recovery Time to ORP 281 was Approx. 14 hours

Food Slurry Add---Initial ORP 279
After add 215
Difference 64
Time to minimum approx. 30 min
Recovery time to ORP 270 was approx. 6 hours

Data from display Tank (This data represents the general behavior of adding the slurry)

Food Slurry Add---Initial ORP 284
After add 167
Difference 117
Time to minimum approx. 10 min
Recovery time to ORP 292 was approx. 5 hours

I don't have any data for the display tank adding H2O2

The recovery time for the two are quite different which might be related to the idea that the H2O2 is doing it's thing (reacting) in the water where as the food slurry is not reacting only making a temporary change to the ORP of the water ...kind of like adding skimate back into the water...I have no idea if this makes sense but they defiantly behave differently...at least in my experiment

 

[Hans-Werner]

I have one more idea: Complexing substances, in biofilm or else.

The report about a different reaction in Instant Ocean: I really don't wanna state something wrong about a competitor's product, but if the numbers I have in mind are right and if the saltwater prepared with Instand Ocean is more or less stable, they should use complexing agents, chelators like EDTA. This may alter the reaction fundamentally. Biofilms may also contain or excrete compexing agents, I am even quite sure they do.

By the way, the normal EDTA complexes with iron to my knowlegde are with Fe(III) and not with Fe(II) as all or nearly all other chelates with iron. I think it is even a reduction process from Fe(III) to Fe(II) that releases the iron from the complex and releases free iron ions. The same is the case with bacterial iron chelators called siderophores. The complex is reduced outside of the bacterium, the iron is released and taken up by the bacteria. These whole processes work with Fe(III) and only final reduction to Fe(II). This is why Fe(II) is no necessity in marine environments and aquaria since Fe(II) is not stable under these conditions anyway. Fe(III) is at least as good and at least as bioavailable because to my knowledge siderophores and similar chelators are specific for Fe(III) and not for Fe(II). This also makes sense because Fe(III) is the only form of iron that is available in the marine (and some other) environment.

Since this involves redox reactions, maybe we can find the solution to our problem here? Maybe try EDTA?

 

[Randy Holmes-Farley]

The report about a different reaction in Instant Ocean: I really don't wanna state something wrong about a competitor's product, but if the numbers I have in mind are right and if the saltwater prepared with Instand Ocean is more or less stable, they should use complexing agents, chelators like EDTA.

I was told by a tech rep that normal Instant Ocean does not contain any chelators, but Reef Crystals does.

 

[Dan_P]

Like hypochlorite and permanganate, persulfate increases the ORP of aquarium water in a repeated dose dependent manner (but less).
The effect from strongest ORP move to least is bleach > permanganate > persulfate.

Each of the first 3 humps is an addition of +5ppm sodium persulfate, the fourth hump is +10ppm.

It seems peroxide is unique in that it simply does not interact with the ORP probe itself, so we only detect it indirectly by what it does to other things.

The trend in ORP response is opposite of what I would have predicted from table in post #101. Should I not necessarily expect to see a trend in ORP reading that correlates with oxidizer strength?

I bet @Rick Mathew would have seen a dip with persulfate Is the construction of your probe also behind not seeing the peroxide dip?

I agree that peroxides affecting the ORP of the system or electrode differently may be part of the solution. Bleach and permanganate have more reaction mechanism options to change the oxidation state of a molecule. Peroxide is pretty much limited to free radical chemistry.

 

[Dan_P]

My current thinking is that it's metals and the details get mediated by the biofilm/ probe effects.


This is my issue with the biofilm idea. It implies that there's some cleaning routine that could be done to a probe showing the drop with h2o2 that would turn off the effect.
Scrub + detergent for biofilms?
Acid to remove deposits?
Ethanol to dissolve other organics?

But no indication so far that cleaning a mature probe turns off the effect.

Good point about cleaning the electrode not giving an unequivocal effect, but we haven’t looked at deliberately fouling an electrode yet. It might not produce a dip with H2O2, but it might be a patentable new type of sensor which I would call the Frankenstein electrode

 

[Randy Holmes-Farley]

The trend in ORP response is opposite of what I would have predicted from table in post #101. Should I not necessarily expect to see a trend in ORP reading that correlates with oxidizer strength?

I bet @Rick Mathew would have seen a dip with persulfate Is the construction of your probe also behind not seeing the peroxide dip?

I agree that peroxides affecting the ORP of the system or electrode differently may be part of the solution. Bleach and permanganate have more reaction mechanism options to change the oxidation state of a molecule. Peroxide is pretty much limited to free radical chemistry.

Not if it is all used up by the redox buffers present.

Analogy is an acid. Muriatic acid is more acidic than acetic acid by many orders of magnitude, but adding 1 mole of either acid into a buffer at pH 8 will give the same pH decrease.

 

[Dan_P]

Not if it is all used up by the redox buffers present.

Analogy is an acid. Muriatic acid is more acidic than acetic acid by many orders of magnitude, but adding 1 mole of either acid into a buffer at pH 8 will give the same pH decrease.

OK, let’s examine my thinking process for flaws.

When I add an oxidizer to a system with no reducible substances, I expect to see the system’s ORP increase.

If I add an oxidizer to the same system with one equivalent of reducible material, I expect to see the system’s ORP increase because I have reduced the amount of species in that system to one with less reducible species. I do not expect the two situations to have the same magnitude of increase, just that the the two end states are more oxidized.

In this simplistic train of thought, there cannot be a situation where adding an oxidizer to a system makes the system look more reduced.

OK, where did my thinking go off the rails?

 

[taricha]

I bet @Rick Mathew would have seen a dip with persulfate Is the construction of your probe also behind not seeing the peroxide dip?

I am still thinking that OPR is a "quantum entrance" into an alternate universe and @taricha is in a different one

but we haven’t looked at deliberately fouling an electrode yet.

I figured out how to get my ORP probe to hop back and forth between universes

All three of the following data runs are with my probe in my display tank until it stabilized with tank water, and then I added ~1ml H2O2 / 10 Gallons.
Before each run I rinsed the probe under tap water and brushed with a test tube brush.

First, a somewhat unfamiliar universe where my ORP drops slightly (-20mV) when adding peroxide to tank water.

Then I placed the probe in Universe Jumping Solution A for a couple of hours, and then rinsed in tap water and back into the tank.
Now we're back in my typical universe where the ORP increases (+20mV) when I add peroxide.

Then I placed the probe into Universe Jumping Solution B for an hour, then rinsed in tap water and back into the tank. Now we're in the universe with Lasse, Rick and the rest of the hobby where peroxide drops ORP by something on the scale of a hundred mV, followed by a multi-hour long recovery.

(Universe Jumping Solution A = my probe storage solution, Universe Jumping Solution B = 1/100 dilution of bleach in distilled water, and before the first run my probe spent the night in tank water with 25ppm sodium persulfate)

 

[Dan_P]

Actually they are much different...Have a look at the data below

Data from the Experiment: (From the charts I posted)

H2O2 add----Initial ORP 290
After add 262
Difference 28
Time to minimum Approx. 30 min
Recovery Time to ORP 281 was Approx. 14 hours

Food Slurry Add---Initial ORP 279
After add 215
Difference 64
Time to minimum approx. 30 min
Recovery time to ORP 270 was approx. 6 hours

Data from display Tank (This data represents the general behavior of adding the slurry)

Food Slurry Add---Initial ORP 284
After add 167
Difference 117
Time to minimum approx. 10 min
Recovery time to ORP 292 was approx. 5 hours

I don't have any data for the display tank adding H2O2

The recovery time for the two are quite different which might be related to the idea that the H2O2 is doing it's thing (reacting) in the water where as the food slurry is not reacting only making a temporary change to the ORP of the water ...kind of like adding skimate back into the water...I have no idea if this makes sense but they defiantly behave differently...at least in my experiment

Thanks for walking me through the data. Here are the points that trip me up.

The food mixing effect reaches a minimum faster on small scale than in the aquarium. Assuming electrode response is equivalent in both offline and aquarium situations, why is the systems mixing time and/or equilibration time slower on small scale? The recovery times being almost the same is about as interesting. The differences in ORP minima does not raise any alarm bells yet. What did I miss here?

The similar time to the minima in the offline experiment is what I would expect, although maybe I shouldn’t. Why would the electrode equilibration time be the same for H2O2 and a food slurry? Mixing time should be the same, but electrode response? Which brings me to a question we have not asked. Do we ever see ORP spikes that look like a flipped H2O2 dip?

 

[Dan_P]

I figured out how to get my ORP probe to hop back and forth between universes

All three of the following data runs are with my probe in my display tank until it stabilized with tank water, and then I added ~1ml H2O2 / 10 Gallons.
Before each run I rinsed the probe under tap water and brushed with a test tube brush.

First, a somewhat unfamiliar universe where my ORP drops slightly (-20mV) when adding peroxide to tank water.

Then I placed the probe in Universe Jumping Solution A for a couple of hours, and then rinsed in tap water and back into the tank.
Now we're back in my typical universe where the ORP increases (+20mV) when I add peroxide.

Then I placed the probe into Universe Jumping Solution B for an hour, then rinsed in tap water and back into the tank. Now we're in the universe with Lasse, Rick and the rest of the hobby where peroxide drops ORP by something on the scale of a hundred mV, followed by a multi-hour long recovery.

(Universe Jumping Solution A = my probe storage solution, Universe Jumping Solution B = 1/100 dilution of bleach in distilled water, and before the first run my probe spent the night in tank water with 25ppm sodium persulfate)

Whoa, the ORP electrode is quite magical Great job!

What on the electrode is being modified? Can you use a tiny paint brush to only treat the exposed metal bits? Only the ceramic plug?

We need to reproduce the effect by treating @Lasse and @Rick Mathew electrodes.

 

[taricha]

What on the electrode is being modified?

Must be deposits that do not rinse or brush off easily. The electrode looks squeaky clean after rinsing and brushing.

We need to reproduce the effect by treating @Lasse and @Rick Mathew electrodes.

My storage solution is hanna hi70300 pH and ORP electrode storage solution.

 

[Lasse]

Something with age is important in the way our probes react

Probe A - I clean it at the red marking

Probe C;s development.

There is a tendency of rising ORP that I do not believe reflect a real rise. Probe A has for long time shown between 390 and 430 mV. After the mechanical cleaning the average value got down and is now slowly rising to the old values.

Probe B and D is still showing erratic values. With Probe B - I think it is a bad probe or port. I will try to figure that out later on.

Sincerely Lasse

 

[Randy Holmes-Farley]

OK, let’s examine my thinking process for flaws.

When I add an oxidizer to a system with no reducible substances, I expect to see the system’s ORP increase.

If I add an oxidizer to the same system with one equivalent of reducible material, I expect to see the system’s ORP increase because I have reduced the amount of species in that system to one with less reducible species. I do not expect the two situations to have the same magnitude of increase, just that the the two end states are more oxidized.

In this simplistic train of thought, there cannot be a situation where adding an oxidizer to a system makes the system look more reduced.

OK, where did my thinking go off the rails?

I cannot disagree with that.

The only caveats are:

1. Adding an oxidizer may not make the ORP rise in a reducer-less environment if the oxidizer itself is not directly and readily impacting an ORP probe. O2 for example.

2. Adding an oxidizer may not make the ORP rise in a reducer environment if the oxidizer itself is not directly and readily impacting the reduced substance. O2 and say, wood for example.

 

[Rick Mathew]

I figured out how to get my ORP probe to hop back and forth between universes

All three of the following data runs are with my probe in my display tank until it stabilized with tank water, and then I added ~1ml H2O2 / 10 Gallons.
Before each run I rinsed the probe under tap water and brushed with a test tube brush.

First, a somewhat unfamiliar universe where my ORP drops slightly (-20mV) when adding peroxide to tank water.

Then I placed the probe in Universe Jumping Solution A for a couple of hours, and then rinsed in tap water and back into the tank.
Now we're back in my typical universe where the ORP increases (+20mV) when I add peroxide.

Then I placed the probe into Universe Jumping Solution B for an hour, then rinsed in tap water and back into the tank. Now we're in the universe with Lasse, Rick and the rest of the hobby where peroxide drops ORP by something on the scale of a hundred mV, followed by a multi-hour long recovery.

(Universe Jumping Solution A = my probe storage solution, Universe Jumping Solution B = 1/100 dilution of bleach in distilled water, and before the first run my probe spent the night in tank water with 25ppm sodium persulfate)

OK...I am on it...Should finish sometime tomorrow

Rick

 

[Rick Mathew]

Thanks for walking me through the data. Here are the points that trip me up.

The food mixing effect reaches a minimum faster on small scale than in the aquarium. Assuming electrode response is equivalent in both offline and aquarium situations, why is the systems mixing time and/or equilibration time slower on small scale? The recovery times being almost the same is about as interesting. The differences in ORP minima does not raise any alarm bells yet. What did I miss here?

The similar time to the minima in the offline experiment is what I would expect, although maybe I shouldn’t. Why would the electrode equilibration time be the same for H2O2 and a food slurry? Mixing time should be the same, but electrode response? Which brings me to a question we have not asked. Do we ever see ORP spikes that look like a flipped H2O2 dip?

OK here is a thought. When I added the food slurry to the "off line" sample it had already been dosed with H2O2 and it interfered with the time to minimum...just a quick thought.