# How quickly does H202 decompose?



## ObiQuiet

In this thread http://www.aquaticplantcentral.com/forumapc/algae/78335-pretty-sure-i-have-clado.html there's a discussion about using H202 (hydrogen peroxide) as a spot treatment for clado algae.

The advice is to limit each treatment to 3ml per 10gal, which makes sense.

Some people say to do a water change after each dose, which certainly wouldn't hurt. Others say that it turns completely harmless in ~ 2 days.

So, I'm curious if a treatment _needs_ to be followed by a water change or not. I'm curious because 
a) H2O2 decomposes to harmless H20 and O2 - which could stay in the tank.
but,
b) It decomposes slowly when there's no catalyst, which is why it can be sold and stored as a 3% solution in distilled water.

Why do I care? Well, if H2O2 decomposes quickly enough to not build up over time, I could spot-treat every N days and fighting algae would be that much more convenient.

On the other hand, if H2O2 doesn't disappear quickly, it should be removed right away before currents spread it around.

Thanks!


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## Seattle_Aquarist

Hi ObiQuiet,

Below is a post I did on treating BGA and BBA with 3% H2O2. I have found that I can dose 1.5 ml per gallon with no signs of ill effects on Cardinals, Apistos, Rasboras, or Corys. I have not tried it on Clado (I have only had Clado once and hope to never have it again). A couple of the key components I have discovered was insuring the algae was at full photosynthesis (in bright light for at least an hour) and turning off water circulation during treatment to insure the H2O2 stays on the algae as long as possible. The chemical reaction (O2 generation) seems to last about 45 minutes; then I turn on my filtration. I only dose once every 24 hours.



> "Last month I mentioned that I had a "dirty little secret". I explained that I did not bring plants to the March meeting because I have been fighting cyanobacteria, also known as Blue-Green Algae (BGA), in one of my tanks and I didn't want to share it with others. After six weeks of trying different methods I seem to be making major headway and will share what is succeeding for me.
> 
> As I write this it has been exactly one week since I finished treating an outbreak of BGA in my 30 gallon aquarium. I believe it started because I let my nitrates (NO3) get too low and missed a couple of water changes. In addition I hadn't cleaned my canister filter for several of months so debris had built up and the flow and circulation had dropped in the tank. Any or all of these conditions could have been the cause for my outbreak.
> 
> Here how I got rid of it. First I worked on the causes. I cleaned my canister filter and added an airstone (I would have used a Koralia Pump or powerhead if I had one) to increase circulation. I increased my fertilizer dosage to 1/8 teaspoon (tsp) of KNO3 (potassium nitrate) and 1/64 tsp of KH2PO4 (monopotassium phosphate) per 10 gallons daily. Lastly I increased my 33% water changes to twice a week.
> 
> Next I went to work on the algae. I siphoned and manually removed as much of the BGA off of the substrate, plants, and hardscape as possible and cleaned the glass. Most of the easy-to-replace plants I threw out. I removed most of the hardscape from the tank, scrubbed it, rinsed it, and put back in place. It was very important to remove as much BGA as possible before doing the next step to minimize oxygen depletion, and fish death, from dying algae.
> 
> I treated the BGA with Hydrogen Peroxide 3.0% (stabilized) solution. Hydrogen Peroxide (H2O2) is available at most grocery stores, pharmacies, and drug stores. I also picked up a 10 ml dosing syringe (for oral dosing of medications) at the drug store when I picked up the H2O2.
> 
> I always did this part of the treatment when I knew I was going to be around for at least a couple of hours afterwards so I could watch my fish for signs of distress. I only treated the tank after the lights (about 2 WPG compact florescent) had been on for at least two hours so photosynthesis was occurring at its' maximum in the BGA. I found that the BGA reaction to the treatment was strongest, and fastest, in the areas of the aquarium with the brightest light (and the most photosynthesis).
> 
> I turned off my filter about 5 minutes prior to treatment to minimize water movement. I dosed the 3.0% (stabilized) H2O2 at the rate of 1.5 ml per gallon of water volume (my 30 gallon tank has 24 gallons of water in it). I put the H2O2 in a glass, filled the 10 ml syringe, stuck my hand in the tank, and s-l-o-w-l-y "painted" the areas where the BGA was heaviest with the thickest "clumps". I added the H2O2 at a rate of about 10 ml per minute so as not to stress the fish too greatly.
> 
> The effect was rapid and dramatic. After several of minutes the areas of BGA I had "painted" with the H2O2 began to bubble (gas) and started to turn a rusty brown. After about 30 minutes the "painted" areas were bubbling intensely and had turned a definite brown color while other areas of the tank (where I had not "painted") were also bubbling (but not as intensely) and starting to turn rusty brown. After about an hour the water in the tank had a slight "rusty" color, the areas or BGA I had "painted" were a definite brown, areas of BGA that were heavy but had not been "painted" had some of the brown, and plant leaves that had a film of BGA and a film of brown. After one hour I turned the filter and airstone back on and continued to observe the fish for any signs of distress for an additional hour. After a couple of hours the water cleared and the fish become more active. After 24 hours the areas I had "shot" had turned a grey color and the BGA appeared dead.
> 
> I followed the same procedure for dosing the next day again dosing the areas with heaviest algae that was yet dead. The dosed areas bubbled and turned rusty but there was not as much bubbling and rust in other areas (I think because areas with a light coating of BGA had been killed on the first day), the water did not changed color as much, and bubbling activity and any discoloration cleared in about 2 hours.
> 
> Each day for a two week period I followed the procedure I described above. Each day the amount of BGA diminished and after about 8 days the BGA appeared to be gone. I continued the treatment for an additional four (4) days just to be sure there was no residual "hiding" in the crevasses of my driftwood or under plant leaves. It was not necessary to hit the BGA directly with the hydrogen peroxide to kill it. For example, on the edges and undersides of plant leaves I did not "paint" the areas but after about 5 days the BGA had turned rusty brown, was breaking away from the leaves, and was falling off.
> 
> As a side note I also had an outbreak of Black Brush Algae (BBA) in this same tank; probably due to the low CO2. The treatment described above worked on it as well, but the BBA did have to be "painted" to die and areas in bright light responded the best to treatment."


Hope this helps


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## ObiQuiet

Seattle_Aquarist said:


> Hope this helps


Yes, thank you. Your dose seems to be higher than others (1.5ml per 1gal, versus 3ml per 10gal).

I'm devising an experiement to test the longevity of H2O2 in aquarium water:
1. Put 5ml of tank water in a test tube. No debris, no visible algae, just plain tank water.
2. Add 1ml of 3% H2O2 solution.

This is a much higher concentration than one would see in the tank.

3. Wait 2 days.
4. Add some stands of algae to the test tube.

If there is bubbling, then the H2O2 is still present => repeat the experiment at a lower concentration or wait more days.

If there is no bubbling, then conclude:
a) that the H2O2 has decomposed, 
b) that it is safe to skip the water changes if one limits spot treatments of algae to < 1.5ml/gal every other day.

Thoughts?


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## Seattle_Aquarist

Hi ObiQuiet,

It sounds like an interesting experiment, my guess is because hydrogen peroxide is not a very stable compound it will not remain viable in aquarium water for very long.

I do not do additional water changes after treatments; however I do a 50% weekly water change.


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## cliffclof

In a Killifish hatching tank I added a decent amount of H2O2 before I realized H2O2 does not oxygenate water. This was in a small 700 mL container that had some boiled Peat moss in the substrate. It was in solution for quite some time. about 48 hours at least. So for my personal self I am careful to dose hydrogen peroxide unless I really have to.


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## ObiQuiet

Ok, I did the above experiement, with these additions:

1. One sample was mixed then aged for 2 days, another for 1 day, and a third for just an hour.

2. I capped the test tubes and put them in the tank, so that temperature and light would not be a factor, just in case.

3. The ratios were (5ml water : 1ml H2O2) in all three cases.

The subjective results:
I added small amounts of clado to each tube. The 1 hour and 1 day old mixtures bubbled about the same amount. The 2-day old mixture was between 1/3 and 1/2 as "potent" -- it still bubbled, but not as much as the other two.

Conclusion: This amount of H2O2 does not decompose fully in aquarium water after 2 days. Thf, I cannot conclude that lower concentrations are gone in at most 2 days without trying them too.


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## barclaya

My slow grow plant and driftwood have BBA. but not to much, I try to trim the infected leaf( mostly on the bottom part). but the BBA keep coming back on another leaf. I will try Your advise using H2O2. thanks,


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## ObiQuiet

FWIW, I adjusted & re-ran this experiment:

* I added 1 drop of H2O2 to 5ml of tank water in each of 8 test tubes, and capped them. (This is close to the concentration of 3ml per 10gal mentioned above.)

* Each day, I added yeast to one tube to see if H2O2 was still present. I used yeast since the bubbling is much more than with algae, so at this lower concentration of H2O2 I could still have a visible result.

* Only after 7 days was there significant decrease in the amount of bubbling. 

This doesn't mean (I think) that H2O2 stays present that long in a real tank. In a real tank it would continuously come into contact with new material to react with, which doesn't happen in a test tube.

Anyway, I don't see that this line of experiment was very helpful... just a little interesting to me.


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## Seattle_Aquarist

ObiQuiet said:


> This doesn't mean (I think) that H2O2 stays present that long in a real tank. In a real tank it would continuously come into contact with new material to react with, which doesn't happen in a test tube.


Hi ObiQuiet,

I think you have hit the nail on the head, in an aquarium there is a constant supply if material available for the H2O2 to oxidize; not so in a test tube.


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## cbwmn

cliffclof said:


> In a Killifish hatching tank I added a decent amount of H2O2 before I realized H2O2 does not oxygenate water. This was in a small 700 mL container that had some boiled Peat moss in the substrate. It was in solution for quite some time. about 48 hours at least. So for my personal self I am careful to dose hydrogen peroxide unless I really have to.


H2O2 decoposes into H20 (water) and oxygen.

http://en.wikipedia.org/wiki/Hydrogen_peroxide
Charles


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## cliffclof

cbwmn said:


> H2O2 decoposes into H20 (water) and oxygen.
> 
> http://en.wikipedia.org/wiki/Hydrogen_peroxide
> Charles


Yes it sure does, but where does that oxygen go? There are better ways to oxygenate water.

PS. This thread and you gave me a great idea to clean out my RO DI and storage tank with H2O2. No more anaerobic bacteria,, shweet.


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## Seattle_Aquarist

Hi cliffclof,

When the H2O2 oxidizes in my tanks the O2 is released as a fine mist of bubbles where the oxidation is occuring.


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