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

[Randy Holmes-Farley]

All of you miss one thing in this thread

I have test with RODI water, with tap water, with newly mixed saltwater and old saltwater in a bucket and not get the dip of redox. 5 ml H2O2 in 5 L of liquid every time. All have been done with new clean electrodes. The same amount of peroxide to my 300 L aquarium give a huge dip with an old electrode - but no dip at all with a new.

I have use 4 electrodes - 1 old and 3 new

This make no sense but it is a result of tests

Sincerely Lasse

To expand on my assertion that trace metals may be the explanation:

It is my expectation the some of the trace elements in artificial seawater are added in the reduced for because of the higher solubility. Ferrous sulfate, for example, instead of ferric salts.

Thus, if copper or another redox active element is in the reduced form in the new seawater (not necessarily in the recipe, but in the mixed seawater where they can react with one another, for example, ferrous iron possibly converting copper++ to copper +), then the mixture may already be in a more reduce form (hence the low ORP of new artificial seawater) and adding somethign that could reduce it more (like H2O2) would not be expected to show a dip because maybe the pertinent ion(s) is(are) already fully reduced.

 

[Lasse]

I do not think it disputes the trace metal hypothesis.

No - maybe do it a little weaker at least as single reason

Sincerely Lasse

 

[Lasse]

I will do a new test set up. I move my second computer (the one I have used for the bucket) with one 2 weeks old electrode working in the bucket with old saltwater and one that have been in use for 1 week before. After this I have four electrodes in my main setup. All with different age in action.

Sincerely Lasse

 

[Dan_P]

I don't agree it's magic at all.

ORP is a ratio of oxidizers to reducers and the ratio is unchanged with dilution. The Nernst equation shows this very clearly:

Nernst equation - Wikipedia

en.wikipedia.org

.

For example, if copper is the only ion impacting ORP in a solution, then the ORP is exactly determined by the ratio of Cu+ to Cu++.

That ratio is unchanged by dilution, so the ORP is also unchanged by dilution.

If hydrogen peroxide is altering the ratio of Cu+ to Cu++, is the degree of that change int he ratio determined by the absolute concentration of copper?

maybe, maybe not. Maybe it is controlled primarily by the relative oxidizing and reducing capability of the H2O2 and the copper.

It would take a much deeper understanding of the processes to even work out on paper what dilution would do, IMO.

You did not address the the magnitude of the dip. If that is not concentration dependent then magic is back on the table.

 

[Randy Holmes-Farley]

You did not address the the magnitude of the dip. If that is not concentration dependent then magic is back on the table.

I cannot agree.

How do you conclude that the magnitude of the dip when adding peroxide to copper would necessarily depend on the total copper concentration?

I agree that if there's no copper, there will be no dip from that mechanism, but otherwise, I do not think the analysis is not so straightforward.

Assuming nothing else is going on (very sketchy assumption), a redox reaction will proceed until the ratio of reactants and products reach a equilibrium ratio based on the relative oxidizing and reducing ability of the four species involved (the Nernst equilibrium). SInce ORP is determined by that ratio (or a ratio of just the copper if the peroxide and O2 are not in redox equilibrium with the electrode), then the final ORP may depend primarily on the relative oxidizing and reducing abilities of Cu+, Cu++, peroxide, and whatever is the oxidized form of the peroxide (O2?).

 

[Dan_P]

I cannot agree.

How do you conclude that the magnitude of the dip when adding peroxide to copper would necessarily depend on the total copper concentration?

I agree that if there's no copper, there will be no dip from that mechanism, but otherwise, I do not think the analysis is not so straightforward.

Assuming nothing else is going on (very sketchy assumption), a redox reaction will proceed until the ratio of reactants and products reach a equilibrium ratio based on the relative oxidizing and reducing ability of the four species involved (the Nernst equilibrium). SInce ORP is determined by that ratio (or a ratio of just the copper if the peroxide and O2 are not in redox equilibrium with the electrode), then the final ORP may depend primarily on the relative oxidizing and reducing abilities of Cu+, Cu++, peroxide, and whatever is the oxidized form of the peroxide (O2?).

Yes, good point! I will concede.

The practical upshot of dilution is that the ORP probe will fail to detect the transition metal effect before it reaches zero atoms. If the dilution of tank water does not alter the ORP dip response, the effect cannot be from the transition metal or metals. If it does change the dip to a rise, we still have work to do, like using ultra pure NaCl to dilutrpe transition metals but not salinity.

 

[Dan_P]

No - maybe do it a little weaker at least as single reason

Sincerely Lasse

Do you think the ORP probe can detect changes in the ratio of transition metal oxidation states at the ppb level? I would say lack of sensitivity and stability of the ORP probe is an even stronger case against a transition metal effect.

 

[Lasse]

It is measuring in mV and 1 mV is probably equal to x transitions as I can understand. What x is - no idea.

Sincerely Lasse

 

[taricha]

Keep in mind that it seems everyone observes this dip. Does everyone fortuitously have the same amounts or ratios of trace elements?

*raises hand* Everyone but me observes the dip in tank water. My tank water ORP goes up with an h2o2 dose. Part of my interest in the mechanism is that it doesn't happen in my tank water, and I couldn't get it to happen.
More interestingly, the effect in my tank water is variable:
May 2020 - small ORP move up at 1ml h2o2/10L , larger if 10x dose
May 26, 2020 - different h2o2 doses - ORP goes up.
Left it in for weeks , let it grow all kinds of grunge on the probe, ORP still went up with h2o2 addition. Tried like 4 different h2o2 sources, ORP up for all of them.

Jan 2021, Tried to duplicate - and found that ORP in my tank water has flipped and goes down with h2o2 like the rest of the hobby.
Currently Aug 20201, my ORP goes up with h2o2 additions to my tank water, the way it has in the past for me. See below data....

here's my tank water (1L, glass beaker, stirrer) 0.1mL h2O2 added at 7.5 min.

Proposed experiment: dose varying amounts of H2O2 to RODI containing various amounts of NaCl. A factorial design would work well here.

ORP doesn't go down in newly mixed saltwater for me or Lasse. So I'm not sure what NaCl would illuminate. But I'll post some beaker tests you may enjoy.

I have test with RODI water, with tap water, with newly mixed saltwater and old saltwater in a bucket and not get the dip of redox. 5 ml H2O2 in 5 L of liquid every time. All have been done with new clean electrodes.

If it's really the external biofilm making the new and old electrodes different - then there must exists some cleaning process that would make the old electrode act like the new ones.
And it would mean you could take the old electrode and put it in other media that don't show the effect like new saltwater and generate the familiar ORP drop effect. It ought to be portable with the biofilm on the probe, if the biofilm effect is strong.

The same amount of peroxide to my 300 L aquarium give a huge dip with an old electrode - but no dip at all with a new.

to be clear you are adding 5mL 3% peroxide in your bucket tests to 5L water, and in your tank you are adding 5mL in 300L? I don't think you are saying you put 5mL/ L of h2o2 in your tank?

 

[taricha]

here you go, @Dan_P some beaker tests of what ORP does with new Instant Ocean mixed to 1.026 in a 1L beaker on a stirrer. The 1L of I.O. is getting dosed with 0.01mL of 3% H2O2. A common hobby dosage of h2o2 is 1mL/10 gallons. (this would be about 0.4mL / 10 gallons.)

This is initially, within the first hour of mixing, after the probe settled in a bit, the h2o2 was added at ~22min. The peroxide causes an increase of 12 mV from ~150 to ~162 over the next 20 min.

after ~15 hours (of gentle mixing in the beaker) the dose was repeated...

looks like an ORP increase of ~9 mV from ~178 to ~187 over about 20 minutes.


After 9 more hours of more vigorous mixing... ( I figured out how to turn the noise way down on my device)

I split the same 0.01mL h2o2 in half. One half at ~7min and the other half again at ~30min. Total rise of ~6mV over 20 minutes.

and here's the entire picture over this 25 hours....

Frankly, everything seems to be behaving consistent with expectations.
Very non-magical.
ORP increases with continued stirring, and increases faster in the 20min after H2O2 additions. Each successive dose (at progressively higher ORP) gives a smaller increase in ORP than those previous. No sign of any longer time rebound in ORP, it continues going higher.

No sign of the familiar ORP drop that other people see in tank water (but who knows if my educational single-junction probe acts like other people's reefing double-junction probe.)
I wonder if someone who gets the ORP drop in their tank water (@Rick Mathew) could be persuaded to replicate with his ORP probe. he finds the normal drop in tank water, so I wonder if he gives the probe a good scrub and tries this in new 1.026 I.O. would he see the same general behavior?

Overall,my data with new I.O. looks mostly like it's measuring something real - more things are being oxidized by h2o2 than reduced, and seems pretty decently in line with Randy's expectations from below (as I understand it).

It is my expectation the some of the trace elements in artificial seawater are added in the reduced for because of the higher solubility. Ferrous sulfate, for example, instead of ferric salts.

Thus, if copper or another redox active element is in the reduced form in the new seawater (not necessarily in the recipe, but in the mixed seawater where they can react with one another, for example, ferrous iron possibly converting copper++ to copper +), then the mixture may already be in a more reduce form (hence the low ORP of new artificial seawater) and adding somethign that could reduce it more (like H2O2) would not be expected to show a dip because maybe the pertinent ion(s) is(are) already fully reduced.

 

[Rick Mathew]

here you go, @Dan_P some beaker tests of what ORP does with new Instant Ocean mixed to 1.026 in a 1L beaker on a stirrer. The 1L of I.O. is getting dosed with 0.01mL of 3% H2O2. A common hobby dosage of h2o2 is 1mL/10 gallons. (this would be about 0.4mL / 10 gallons.)

This is initially, within the first hour of mixing, after the probe settled in a bit, the h2o2 was added at ~22min. The peroxide causes an increase of 12 mV from ~150 to ~162 over the next 20 min.

after ~15 hours (of gentle mixing in the beaker) the dose was repeated...

looks like an ORP increase of ~9 mV from ~178 to ~187 over about 20 minutes.


After 9 more hours of more vigorous mixing... ( I figured out how to turn the noise way down on my device)

I split the same 0.01mL h2o2 in half. One half at ~7min and the other half again at ~30min. Total rise of ~6mV over 20 minutes.

and here's the entire picture over this 25 hours....

Frankly, everything seems to be behaving consistent with expectations.
Very non-magical.
ORP increases with continued stirring, and increases faster in the 20min after H2O2 additions. Each successive dose (at progressively higher ORP) gives a smaller increase in ORP than those previous. No sign of any longer time rebound in ORP, it continues going higher.

No sign of the familiar ORP drop that other people see in tank water (but who knows if my educational single-junction probe acts like other people's reefing double-junction probe.)
I wonder if someone who gets the ORP drop in their tank water (@Rick Mathew) could be persuaded to replicate with his ORP probe. he finds the normal drop in tank water, so I wonder if he gives the probe a good scrub and tries this in new 1.026 I.O. would he see the same general behavior?

Overall,my data with new I.O. looks mostly like it's measuring something real - more things are being oxidized by h2o2 than reduced, and seems pretty decently in line with Randy's expectations from below (as I understand it).

Will give it a shot...Don't use IO but will try with Red Sea mixed to 1.026...

 

[Dan_P]

*raises hand* Everyone but me observes the dip in tank water. My tank water ORP goes up with an h2o2 dose. Part of my interest in the mechanism is that it doesn't happen in my tank water, and I couldn't get it to happen.
More interestingly, the effect in my tank water is variable:
May 2020 - small ORP move up at 1ml h2o2/10L , larger if 10x dose
May 26, 2020 - different h2o2 doses - ORP goes up.
Left it in for weeks , let it grow all kinds of grunge on the probe, ORP still went up with h2o2 addition. Tried like 4 different h2o2 sources, ORP up for all of them.

Jan 2021, Tried to duplicate - and found that ORP in my tank water has flipped and goes down with h2o2 like the rest of the hobby.
Currently Aug 20201, my ORP goes up with h2o2 additions to my tank water, the way it has in the past for me. See below data....





ORP doesn't go down in newly mixed saltwater for me or Lasse. So I'm not sure what NaCl would illuminate. But I'll post some beaker tests you may enjoy.



If it's really the external biofilm making the new and old electrodes different - then there must exists some cleaning process that would make the old electrode act like the new ones.
And it would mean you could take the old electrode and put it in other media that don't show the effect like new saltwater and generate the familiar ORP drop effect. It ought to be portable with the biofilm on the probe, if the biofilm effect is strong.


to be clear you are adding 5mL 3% peroxide in your bucket tests to 5L water, and in your tank you are adding 5mL in 300L? I don't think you are saying you put 5mL/ L of h2o2 in your tank?

You and Lasse might be the only ones to dose H2O2 to a tank water sample rather than to the tank. I couldn’t even begin to weave a story around the differences. Just to close the loop, I am afraid you will have to add H2O2 to your aquarium while monitoring ORP (I assume the January observation of a dip was again in a sample of water).

 

[Dan_P]

here you go, @Dan_P some beaker tests of what ORP does with new Instant Ocean mixed to 1.026 in a 1L beaker on a stirrer. The 1L of I.O. is getting dosed with 0.01mL of 3% H2O2. A common hobby dosage of h2o2 is 1mL/10 gallons. (this would be about 0.4mL / 10 gallons.)

This is initially, within the first hour of mixing, after the probe settled in a bit, the h2o2 was added at ~22min. The peroxide causes an increase of 12 mV from ~150 to ~162 over the next 20 min.

after ~15 hours (of gentle mixing in the beaker) the dose was repeated...

looks like an ORP increase of ~9 mV from ~178 to ~187 over about 20 minutes.


After 9 more hours of more vigorous mixing... ( I figured out how to turn the noise way down on my device)

I split the same 0.01mL h2o2 in half. One half at ~7min and the other half again at ~30min. Total rise of ~6mV over 20 minutes.

and here's the entire picture over this 25 hours....

Frankly, everything seems to be behaving consistent with expectations.
Very non-magical.
ORP increases with continued stirring, and increases faster in the 20min after H2O2 additions. Each successive dose (at progressively higher ORP) gives a smaller increase in ORP than those previous. No sign of any longer time rebound in ORP, it continues going higher.

No sign of the familiar ORP drop that other people see in tank water (but who knows if my educational single-junction probe acts like other people's reefing double-junction probe.)
I wonder if someone who gets the ORP drop in their tank water (@Rick Mathew) could be persuaded to replicate with his ORP probe. he finds the normal drop in tank water, so I wonder if he gives the probe a good scrub and tries this in new 1.026 I.O. would he see the same general behavior?

Overall,my data with new I.O. looks mostly like it's measuring something real - more things are being oxidized by h2o2 than reduced, and seems pretty decently in line with Randy's expectations from below (as I understand it).

Great blast of data! Thank you.

The increase in mV is in the correct direction, but tiny. Bleach is a little weaker oxidizer than H2O2 and I know you were monitoring Cl2 demand experiments with ORP. Was the bleach also giving you tiny increases in mV too? I can’t remember.

By the way, would you expect to see the oxidation or reduction of ppb level transition metals with your ORP probe?

 

[taricha]

Just to close the loop, I am afraid you will have to add H2O2 to your aquarium while monitoring ORP (I assume the January observation of a dip was again in a sample of water).

Those observations were all checked in the tank as well - went same way as tank water in a beaker.
It was just that one time, in January, adding h2o2 to my tank dropped the ORP - rechecked that every way I could think of. The other times (including now) that I played with ORP + h2o2 before or since, it went the other direction - up, unlike the rest of the hobby.

The increase in mV is in the correct direction, but tiny. Bleach is a little weaker oxidizer than H2O2 and I know you were monitoring Cl2 demand experiments with ORP. Was the bleach also giving you tiny increases in mV too? I can’t remember.

No comparison between bleach and peroxide. Bleach blasts the ORP high in a dose-dependent way that also depends on the contents of the water. In distilled water the tiniest concentration of bleach will push the ORP to 600+, or higher if you're willing to wait longer...

I later learned that kink in the Instant Ocean graph (yellow) is because I goofed and was mixing up I.O. contaminated with ammonia. I changed my water sources after.

By the way, would you expect to see the oxidation or reduction of ppb level transition metals with your ORP probe?

I was just thinking that since the change is so tiny, once this beaker of new I.O. settles down, I'll split it and add ~10ppb Cu (from CuCl2) to one half. See if the ORP can tell the difference.

 

[taricha]

Will give it a shot...Don't use IO but will try with Red Sea mixed to 1.026...

Thanks, that and my ICP test coming up might help convince me whether my water is weird or my ORP probe is weird. Also, your Red Sea ought to go similarly to Lasse's if yall's ORP probes are measuring real things.

 

[Lasse]

Things getting more interesting.

1/8 I started to test in one bucket of RO water and one bucket of Tap water. Tqo brand new GHL Redox probes. Not dip of ORP when adding 5 ml H2O2. In my DT - the addition create a dip.

11/8 - I put electrode B into a storage solution and start testing with only one redox probe (C) - both in fresh mixed salt water and in my old tank water (but in a bucket) - no apparently dip in redox when I add 5 ml 12% H2O2. I let electrode C left in the bucket.

12/8 I install a brand new electrode (D) beside my old electrode (A) in the sump. Addition of 5 ml H2O2 create a dip in the old electrode (A) but not in the new (C)

Yesterday - I took electrode B and C and put them in my DT. B only used for 11 days - storage 10 days - storage and C used for 21 days in a row.

In DT for the moment

Placed in sump
Probe A (old - been there for + 1 year
Probe D (new - used in DT for 10 days

Place in the tank
Probe B (New - used for 11 days - storage 10 days)
Probe C (New - used for 21 days in a row)

Charts - Probe A - my old in the sump Red - addition of 5 ml H2O2 (red circle) Blue circle reaction to automatically feed of frozen food

Probe D a 10 day old probe placed in the sump Red - addition of 5 ml H2O2 (red circle)

No dip in this electrode at all

Probe B (New - used for 11 days - storage 10 days) In DT but in the back . It is still rather noisy but you can see a tendency to dips every feeding (blue staples). No response to addition of H2O2

Probe C (New used for 21 days but only 1 day in the DT) placed just close to probe B. Addition of H2O2 red circle. It seems like this probe react to the automatically feeding 10:00; 10:30; 11:00; 12:00 and every hour to 18:00 but not to the addition of H2O2 !

This rise more questions than it answers. I´ll testing one possible error at feeding time.

But till now - it seems that time in aquarium water have impact on how the probes react but which mechanisms involved - I can´t say

Sincerely Lasse

 

[Dan_P]

Those observations were all checked in the tank as well - went same way as tank water in a beaker.
It was just that one time, in January, adding h2o2 to my tank dropped the ORP - rechecked that every way I could think of. The other times (including now) that I played with ORP + h2o2 before or since, it went the other direction - up, unlike the rest of the hobby.



No comparison between bleach and peroxide. Bleach blasts the ORP high in a dose-dependent way that also depends on the contents of the water. In distilled water the tiniest concentration of bleach will push the ORP to 600+, or higher if you're willing to wait longer...

I later learned that kink in the Instant Ocean graph (yellow) is because I goofed and was mixing up I.O. contaminated with ammonia. I changed my water sources after.




I was just thinking that since the change is so tiny, once this beaker of new I.O. settles down, I'll split it and add ~10ppb Cu (from CuCl2) to one half. See if the ORP can tell the difference.

Good move on copper addition. How about Fe (II)?

 

[Dan_P]

Things getting more interesting.

1/8 I started to test in one bucket of RO water and one bucket of Tap water. Tqo brand new GHL Redox probes. Not dip of ORP when adding 5 ml H2O2. In my DT - the addition create a dip.

11/8 - I put electrode B into a storage solution and start testing with only one redox probe (C) - both in fresh mixed salt water and in my old tank water (but in a bucket) - no apparently dip in redox when I add 5 ml 12% H2O2. I let electrode C left in the bucket.

12/8 I install a brand new electrode (D) beside my old electrode (A) in the sump. Addition of 5 ml H2O2 create a dip in the old electrode (A) but not in the new (C)

Yesterday - I took electrode B and C and put them in my DT. B only used for 11 days - storage 10 days - storage and C used for 21 days in a row.

In DT for the moment

Placed in sump
Probe A (old - been there for + 1 year
Probe D (new - used in DT for 10 days

Place in the tank
Probe B (New - used for 11 days - storage 10 days)
Probe C (New - used for 21 days in a row)

Charts - Probe A - my old in the sump Red - addition of 5 ml H2O2 (red circle) Blue circle reaction to automatically feed of frozen food

Probe D a 10 day old probe placed in the sump Red - addition of 5 ml H2O2 (red circle)

No dip in this electrode at all

Probe B (New - used for 11 days - storage 10 days) In DT but in the back . It is still rather noisy but you can see a tendency to dips every feeding (blue staples). No response to addition of H2O2

Probe C (New used for 21 days but only 1 day in the DT) placed just close to probe B. Addition of H2O2 red circle. It seems like this probe react to the automatically feeding 10:00; 10:30; 11:00; 12:00 and every hour to 18:00 but nit to the addition of H2O2 !

This rise more questions than it answers. I´ll testing one possible error at feeding time.

But till now - it seems that time in aquarium water have impact on how the probes react but which mechanisms involved - I can´t say

Sincerely Lasse

I agree the data is difficult to explain but I think you generated fantastic results.

 

[Lasse]

About graph for probe C. I thought that I saw a dip when I looked at the measuring IRL but it seems that the graph did not pick it up. I did a test a little bit later and get an indication that it react - a litle bit later but still a reaction.

If I look at both graph (B and C) together - you can see that they follow each other rather well but it is dificult to see in the graph that is unstable. Red = H2O2 addition. Note - it is not the same scale on the Y axis - however the time scale is the same

Sincerely Lasse

 

[taricha]

Lasse this is really good work.

my interpretation of your last round of data - Probe D (for dud) is not measuring anything.

Probe A and C are really showing out. I did not fully appreciate that you were seeing a drop of multiple hundreds of mv with h2o2 addition.

Charts - Probe A - my old in the sump Red - addition of 5 ml H2O2 (red circle) Blue circle reaction to automatically feed of frozen food

Probe C (New used for 21 days but only 1 day in the DT) placed just close to probe B. Addition of H2O2 red circle. It seems like this probe react to the automatically feeding 10:00; 10:30; 11:00; 12:00 and every hour to 18:00 but not to the addition of H2O2 !

Probe A and C together make a really good case that the ORP moves with h2o2 that are seen in a tank are hyper-local effects between water chemistry and the Probe surface itself.
The feeding: at first glance looks like the new probe is super sensitive to the feeding and the old one barely cares - but If you think about the timing and location, the discrepancy shrinks. Probe C sees ORP drops with feeding of ~100mv, but the recovery is fast, maybe 80% recovered in 20 min. Given where the feeding happens and the mixing between sump and display, probe A and C are probably both accurately reflecting the effect of the feeding at their locations in the tank. You can see this in that the long term cumulative effect of the feeding from 10:00 to 18:00 is a drop of ~40mV and both probes A & C show this.

If I look at both graph (B and C) together - you can see that they follow each other rather well but it is dificult to see in the graph that is unstable.

Nice demonstration. Probe B is waking up perhaps.

I wonder if probe C and A together are telling us that the h2o2 indeed causes substances measured by ORP to be chemically reduced in the water, but that over time "conditioning" of the probe accumulates these reducible substances to higher concentration on the probes themselves. But again, that idea implies that there is some cleaning/dissolving routine that could be done to an old probe to make it act like a new one - much less responsive to h2o2.