ORP Drop When Dosing H2O2

[Emerson]

I read the ORP article posted on Reefkeeping; very informative. ( http://reefkeeping.com/issues/2003-12/rhf/feature/ ).

My 75 gal Mixed Ed Reef will stay around 400-425 mv, as measured on a 2016 Apex, when left to itself with a Vertex skimmer running.

Table 2 in the article lists hydrogen peroxide (H2O2) as an oxidizer, as I understand dosing would increase ORP when added. I have been dosing 3% H2O2 at 1ml/gal trying to get a cyano outbreak under control and seems to have worked with no ill effects. The only other effect, aside from seeing cyano virtually disappear, is a temporary partial closure of zoanthids.

My question is this: when I dose H2O2, it drops ORP by about 200 mv. As H2O2 is an oxidizer, is this because it is reacting with the organics (cyano, algae, producing reducers, to hopefully being skimmed?) causing an ORP drop? After a few minutes ORP immediately begins to recover, usually dropping to about 200 mv then climbing back to tank normal of ~425 mv.

Thanks in advance @ Randy Holmes-Farley and others for your replies.

 

[Randy Holmes-Farley]

I've always wondered about this effect, which is typically observed. It is not intuitive. H2O2 can act as a reducing agent, but I don't think it would lower ORP. That said, ORP is a complicated beast, and not all oxidizing and reducing compounds interact with an ORP probe to show their effects (O2, for example, which is highly oxidizing but doesn't itself react at an ORP probe, typically).

All I can think of is that the peroxide kills microorganisms and breaks open cell membranes, spilling low redox chemicals into the water.

Another possibility (less likely) is stabilizers in the hydrogen peroxide, which themselves might impact ORP.

If you have a chance, you might stick your ORP probe into the bottle of hydrogen peroxide and see what it reads. I've not seen anyone do that.

 

[Emerson]

Thanks!

 

[Blue Carbon Reefing]

@Randy Holmes-Farley This is interesting the reduction i see every time I dose H2O2. Here is what mine looks like today. I will stick the orp probe in a bottle of Hydrogen Peroxide tonight and see what it goes to. Has anyone done this for you yet? I see you posted this a month ago.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley This is interesting the reduction i see every time I dose H2O2. Here is what mine looks like today. I will stick the orp probe in a bottle of Hydrogen Peroxide tonight and see what it goes to. Has anyone done this for you yet? I see you posted this a month ago.

Not yet. Still waiting! :)

It's a super fast drop that you show!

 

[Blue Carbon Reefing]

Not yet. Still waiting! :)

It's a super fast drop that you show!

So when taking the ORP probe and putting it directly into a bottle of hydrogen peroxide it instantly dropped to 293- to 303 and remained steady in that range. It is interesting because when I add the H2O2 to the tank water my ORP goes down to the low 200's. Last night down to 205 as the min.

Any thoughts?

 

[Blue Carbon Reefing]

@Randy Holmes-Farley I wanted to make sure you saw this post above

 

[Randy Holmes-Farley]

I see it.

Can't say I understand it, but thank's for posting it. :D

 

[DoberDude]

I've always wondered about this effect, which is typically observed. It is not intuitive. H2O2 can act as a reducing agent, but I don't think it would lower ORP. That said, ORP is a complicated beast, and not all oxidizing and reducing compounds interact with an ORP probe to show their effects (O2, for example, which is highly oxidizing but doesn't itself react at an ORP probe, typically).

All I can think of is that the peroxide kills microorganisms and breaks open cell membranes, spilling low redox chemicals into the water.

Another possibility (less likely) is stabilizers in the hydrogen peroxide, which themselves might impact ORP.

If you have a chance, you might stick your ORP probe into the bottle of hydrogen peroxide and see what it reads. I've not seen anyone do that.

Actually, the reason peroxide can cause ORP readings to drop is because it is a disporportionating oxiding reagent. In a process called Fenton's reagent, peroxide will alternatvely oxidize and reduce iron concurrently, thereby releasing hydroxy radicals that do the heavy lifting. On it's own in water with no masking constituents, the ORP probe struggles to figure out which pronouns the peroxide is using. To borrow a current event term.