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

[Randy Holmes-Farley]

@Randy Holmes-Farley I want to sterilize my probe in order to know if it is a biofilm reaction or not. But if I use a liquid to this (eg. ethanol) I maybe change the equilibrium between the internal fluid and the environment and can´t be sure that (if it react as the new probes) if it because of no biofilm or change in the equilibrium. Do you now a "dry" way to sterilize the probe?

Sincerely Lasse

Killing the bacteria may not remove them. Do you want to kill them or remove them?

 

[Lasse]

Remove is probably the best way of test what I want. I have use a toothbrush now but I think that I do not remove all - maybe kill and rinse Maybe use SOS (Save our Saucepans)

Sincerely Lasse















+

Sincerely Lasse

 

[Randy Holmes-Farley]

Most ways of removing bacteria are likely to alter the chemicals directly attached to the probe surface, and hence "restart" the need to equilibrate.

I found that even calibrating my ORP probe had a substantial effect on it, and so putting the probe in calibration fluid and then back into the tank without changing calibration gave a quite different value for the tank.

 

[Dan_P]

That speculation doesn't seem to reflect what is known, IMO.

According to Pankow in "Aquatic Chemsitry Concepts", page 499:

"In natural waters, the group of elements that can play a controlling (his italics) role in determining the redox conditions is rather small. This group includes carbon, oxygen, hydrogen, nitrogen, iron, sulfur, and manganese."

Controlling role at what concentration? The ORP measurement is not infinitely sensitive nor as you have rightly pointed out, are measurements easily interpreted for a complex and uncharacterized mixture of oxidation reduction couples.

 

[Randy Holmes-Farley]

Controlling role at what concentration? The ORP measurement is not infinitely sensitive nor as you have rightly pointed out, are measurements easily interpreted for a complex and uncharacterized mixture of oxidation reduction couples.

I agree that a low enough concentration is not "controlling", and a change in a very low level chemical is not going to be detected. But trace elements such as iron and manganese are expected to be among the controlling ions in natural water, as I quoted above. What controls it depends on what else is there that is might also "control" it.

It would be easy enough to test for a given ion.

Add Cu+ to tank water at some reasonable concentration and see if ORP drops.

Same for Mn+2 and maybe Fe++.

 

[Randy Holmes-Farley]

Controlling role at what concentration? The ORP measurement is not infinitely sensitive nor as you have rightly pointed out, are measurements easily interpreted for a complex and uncharacterized mixture of oxidation reduction couples.

ORP apparently has no problem at all detecting oxidizers and reducers at ppb concentrations:

https://www.mt.com/dam/mt_ext_files/Editorial/Faq/6/FAQ-THOR-ORP-pH_Editorial-Faq_1161357657299_files/orp_measurements.pdf

Other Applications
ORP has excellent sensitivity in low concentrations (ppb ranges) where it is desired to remove an oxidizing or reducing material

 

[Lasse]

Same for Mn+2 and maybe Fe++.

My bold - Did not change anything in RO or Tap water. Did not test with manganese. However I add manganese in my DT 7 times a day. Will check that

Sincerely Lasse

 

[Randy Holmes-Farley]

My bold - Did not change anything in RO or Tap water. Did not test with manganese. However I add manganese in my DT 7 times a day. Will check that

Sincerely Lasse

What form of manganese?

 

[Lasse]

It is Tritons manganese - do not know the form.

Sincerely Lasse

 

[Randy Holmes-Farley]

These folks both see ORP dips on adding trace elements.

Iron and ORP question

I received my triton results which showed an Fe of 0. I dosed 10ml of Kent iron and manganese supplement. Over the next 4 hours I noted a dramatic drop in the ORP. Can someone explain the chemistry? Did I just create rust?? Lol

www.reef2reef.com

ORP and pH daily dips

At precisely 2:45 every afternoon I get a sharp dip in ORP & pH as seen on the Apex. I use 2 Dos pumps that dose Calcium and Alkalinity and the other does transition elements and Acro power. None of the pumps are dosing at that time in the day as checked in the apex log. Does anyone have any...

www.reef2reef.com

 

[Dan_P]

ORP apparently has no problem at all detecting oxidizers and reducers at ppb concentrations:

https://www.mt.com/dam/mt_ext_files/Editorial/Faq/6/FAQ-THOR-ORP-pH_Editorial-Faq_1161357657299_files/orp_measurements.pdf

Other Applications
ORP has excellent sensitivity in low concentrations (ppb ranges) where it is desired to remove an oxidizing or reducing material

ORP apparently has no problem at all detecting oxidizers and reducers at ppb concentrations:

https://www.mt.com/dam/mt_ext_files/Editorial/Faq/6/FAQ-THOR-ORP-pH_Editorial-Faq_1161357657299_files/orp_measurements.pdf

Other Applications
ORP has excellent sensitivity in low concentrations (ppb ranges) where it is desired to remove an oxidizing or reducing material

You fail to point out that the reference is discussing sensitivity at the inflection point when titrating an oxidizer with a reducing agent. The rest of the curve is rather flat on both sides of the this point. Unless you are fortuitously adding the stoichiometric amount of H2O2 to a reducing agent, there is no large response.

 

[Dan_P]

I agree that a low enough concentration is not "controlling", and a change in a very low level chemical is not going to be detected. But trace elements such as iron and manganese are expected to be among the controlling ions in natural water, as I quoted above. What controls it depends on what else is there that is might also "control" it.

It would be easy enough to test for a given ion.

Add Cu+ to tank water at some reasonable concentration and see if ORP drops.

Same for Mn+2 and maybe Fe++.

I agree, the ”H2O2 dip” will be greatly clarified with reproducible observations. I think @Lasse and @taricha are in a position to shed some light on this.

 

[taricha]

It would be easy enough to test for a given ion.

Add Cu+ to tank water at some reasonable concentration and see if ORP drops.

Same for Mn+2 and maybe Fe++.

I agree, the ”H2O2 dip” will be greatly clarified with reproducible observations. I think @Lasse and @taricha are in a position to shed some light on this.

Here is a set of data with 4 day old stirred beaker of Instant Ocean. It was split into subsamples and tested separately. One subsample is just H2O2 added to the I.O., the second was me adding 10ppb Cu to the I.O. before H2O2. The third is an addition of 30ppb Cu to the I.O. before H2O2.

Blue line is showing how just the h2o2 affects the 4 day old I.O.
Then I discarded the subsample and took the second subsample of I.O. dosed 10ppb Cu and after it settled down a bit, added H2O2 at 20min. Then I discarded, took the 3rd subsample of I.O. added 30ppb Cu and when it settled, added H2O2.
The H2O2 doses in each case were 1mL / 40L (10gal).
Copper addition changed the size (smaller), shape (flatter) and timing (much faster) of the ORP increases upon addition of h2o2.

This as I said was with 4 day old I.O. in a beaker. And I think it shows ORP effect of peroxide changing at 10ppb Cu. If the I.O gets depleted of other controlling substances (Fe) as it is aged in a tank, then this amount of Cu or even smaller ones could have a large effect.

(I'll try the same thing with Ferrous sulphate next.)

 

[Lasse]

My old probe after cleaning and logged against Mn additions. Red = cleaning (mechanical)

This electrode shows nearly no connection with dosing Mn. But this probe is in the absolute end of the circulation and the addition take place in the beginning of the circulation. Have not get any comparable result with the other two probes (B and C) Probe D do not show any connections either.

Sincerely Lasse

 

[Dan_P]

Here is a set of data with 4 day old stirred beaker of Instant Ocean. It was split into subsamples and tested separately. One subsample is just H2O2 added to the I.O., the second was me adding 10ppb Cu to the I.O. before H2O2. The third is an addition of 30ppb Cu to the I.O. before H2O2.

Blue line is showing how just the h2o2 affects the 4 day old I.O.
Then I discarded the subsample and took the second subsample of I.O. dosed 10ppb Cu and after it settled down a bit, added H2O2 at 20min. Then I discarded, took the 3rd subsample of I.O. added 30ppb Cu and when it settled, added H2O2.
The H2O2 doses in each case were 1mL / 40L (10gal).
Copper addition changed the size (smaller), shape (flatter) and timing (much faster) of the ORP increases upon addition of h2o2.

This as I said was with 4 day old I.O. in a beaker. And I think it shows ORP effect of peroxide changing at 10ppb Cu. If the I.O gets depleted of other controlling substances (Fe) as it is aged in a tank, then this amount of Cu or even smaller ones could have a large effect.

(I'll try the same thing with Ferrous sulphate next.)

Interesting effect. My money was on no effect. Looking forwards to Fe2+ effect.

How much would you say the salinity changed from the copper addition, tiny?

Just to clarify, when Cu2+ is in solution, a dose dependent decline in the ORP rise is observed when H2O2 is added. It seems there is a larger increase in ORP when H2O2 is added than observed in the last experiment with very noisy data (post #130). Presumably, if Cu was present in that experiment there might not have been an observable effect. Also, a longer observation time would have been interesting to know whether the mV returned to pre-H2O2 addition level. I can’t remember if you have looked at this same experiment in RO water. It might help clarify what phenomenon we are observing.

Thanks for the data fix.

 

[Randy Holmes-Farley]

You fail to point out that the reference is discussing sensitivity at the inflection point when titrating an oxidizer with a reducing agent. The rest of the curve is rather flat on both sides of the this point. Unless you are fortuitously adding the stoichiometric amount of H2O2 to a reducing agent, there is no large response.

I agreed that there is some point in low concentration where adding an oxidizer or reducer to seawater will have no detectable effect. Since neither of us knows what level that is, I think trace metal speciation changes caused by H2O2 remains a perfectly viable explanation. There may also certainly be other explanations.

 

[Rick Mathew]

Here is my contribution to the ORP "Rabbit Hole"

This was conducted using a 1 L container with constant stirring over a 2 day period...The last addition was 12% H2O2

This is day 1...Essentially using the same protocol @taricha used.

This is day 2 with the additions of the frozen food slurry and the 12% H2O2

After returning the probe to my DT in a little less than 2 hours the ORP was at 289-290

Not sure that this adds any real clarity to the work...but none the less here it is...I am starting to suspect "DARK ENERGY"

 

[taricha]

How much would you say the salinity changed from the copper addition, tiny?

Super Tiny. The amount of CuCl2 stock added was 0.0063mL (and then 0.019mL) to 200mL samples.

It seems there is a larger increase in ORP when H2O2 is added than observed in the last experiment with very noisy data (post #130). Presumably, if Cu was present in that experiment there might not have been an observable effect.

You're right that the conditions seem to have shifted between my first day data with the beaker of new I.O. and how the same beaker of I.O. / probe behaved after 3-4 days. I wish I had a definitive answer.

Here's data over the intervening period.

First graph includes all the data in my post number 130, there are 3 h2o2 doses at 0hr, 15hr, and 25hr. Second graph is the beaker left alone slowly stirring over next 3 days. The movement downward could be 3 likely things:
1) h2o2 was still persisting in the beaker and finally disappeared over the next day (this would be consistent with some of your data that h2o2 persists for long periods in pure tank water.)
2) biofilm formation on the probe / other slow conditioning after 1.5-2 days.
3) unhelpful calibration shift in the probe.
...or a combination of the above.

Since the very long term ORP returned close to the initial ORP before any h2o2, I think this is mostly an issue of long residence time of h2o2, meaning that my 2nd and 3rd h2o2 doses were into an I.O. sample that already had h2o2 in it, thus a much smaller movement.

 

[taricha]

Not sure that this adds any real clarity to the work...but none the less here it is...

Lasse adds H2O2 to new Red Sea saltwater (new probe) not much effect - no big ORP drop.
I add H2O2 to new Instant Ocean saltwater (probe from storage) - no big ORP drop (a small rise in fact).
Rick adds H2O2 to new Red Sea saltwater (old probe) big ORP drop just like in tank water.

Seems evidence for the large drop effect being mostly super-local to the probe. Either biofilm, or internal conditioning.

 

[Randy Holmes-Farley]

Lasse adds H2O2 to new Red Sea saltwater (new probe) not much effect - no big ORP drop.
I add H2O2 to new Instant Ocean saltwater (probe from storage) - no big ORP drop (a small rise in fact).
Rick adds H2O2 to new Red Sea saltwater (old probe) big ORP drop just like in tank water.

Seems evidence for the large drop effect being mostly super-local to the probe. Either biofilm, or internal conditioning.

I would just add the complexity that the trace metals that come in a salt mix will almost immediately begin to change redox speciation as they react with each other and with O2 driven oxidants. Thus, the effects one sees, even with a given salt mix, may depend on time after mixing, temperature, and how well aerated it is.