# Hydrogen peroxide ?



## Seattle_Aquarist (Jun 15, 2008)

Hi strangewaters,

I have used hydrogen peroxide (H2O2) to spot treat algae in the past. I found it effective against blue green algae (BGA), thread-type algae, and other softer flat algae types. It seems to have no effect on green spot algae (GSA) nor green dust algae (GDA).


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## Zapins (Jan 7, 2006)

I have found it does works with green spot algae but you need to apply it several times to the same area over several days. The peroxide just burns off the top layer of spot algae but there are several more layers underneath.


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## Complexity (Jan 30, 2008)

i have used H2O2 for years. It's my best friend when fighting algae. What I do is figure out how much H2O2 the tank can handle, load it up in a syringe, stop my filters, and hit the algae with the H2O2. Then turn off the lights. Wait 15 minutes. Turn on the lights and filters. Repeat as needed (I've done it as much as 2x a day). There's no need for a water change since it breaks down from H2O2 to H2O and O (water and oxygen), both of which are fine. A water change may be in order if you kill a lot of algae since all that algae will break down as ammonia, and your current ammonia/nitrite/nitrate cycle may not be able to handle the large load of ammonia from the dead algae. But if you're only working on a small patch of algae, you should be okay just doing your normal weekly water changes.

I have also had good success with doing the full tank method of H2O2. All that means is that I simply dump the H2O2 into the tank (measured amount, of course). Nothing else. The filters distribute the H2O2 throughout the entire tank, filtration system (hoses, etc) and does its job on algae everywhere. Repeat as necessary. It's probably the simplest method of killing out algae that I know of.

I tend to spot treat whenever there is a thicker clump of algae and do the whole tank treatment when there is a more minor breakout throughout the tank. As you gain experience with algae and H2O2, you'll be able to select the method you prefer for various algae outbreaks.

Quick tidbit: H2O2 has been used by professionals to increase the oxygen level in a tank. It can be helpful in times such as long power outages that knock out your filtration (my power was out for almost 2 weeks after a hurricane came through). It's very safe as long as you don't exceed the recommended amount. It's also super cool to watch it in action when it's killing algae!


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## strangewaters (May 13, 2015)

oh wow so if i decided to at some point i can actually do a full tank dose? i have a 55g i did do a spot treatment on a piece of rock and yeah it ate the algae away pretty much. thanks everyone


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## Seattle_Aquarist (Jun 15, 2008)

Hi strangewaters,

Just an FYI, I found I can safely dose 1.5 ml per gallon (approx 1 teaspoon per 3 gallons) and not have an adverse effect on my fish. I have tried this dosage on Cardinal Tetras, Corydoras, and Apistos without the fish showing distress.


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## WaterLife (Jul 1, 2015)

Just curious, in your guy's experience, would that full tank dosing still negatively impact H2O2 sensitive plants such as moss?


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## Aquatic Mag (Dec 29, 2014)

I would suggest spot treating with H2O2 especially if you have sensitive plants in your aquarium. H2O2 full treatment can potentially cause sensitive plants to melt, depending on the concentration being added and the location. We personally turn off our filters and spot treat in locations that have infected areas with a syringe of H2O2. If you have sensitive plants, you might want to pull them out but the golden rule is: "less is more" and with a schedule H2O2 dosing in the daily regimen, it will kill off most algaes like Seattle_Aquarist mentioned without affecting sensitive plants.

Dave has a pretty good intro guide with the H2O2 spot-treating method
https://www.youtube.com/watch?v=geFDaOhCphA


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## jrh (Sep 9, 2007)

So you just spray the H2O2 on a full strength?


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## Aquatic Mag (Dec 29, 2014)

jrh said:


> So you just spray the H2O2 on a full strength?


yeah, we use full strength but not exceeding 2ml per gallon with spot treatments.


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## jrh (Sep 9, 2007)

Cool. I just ordered some 10ml mini spray bottles, so 1 bottle would be the max dose for my 5gal.

Thanks.



Aquatic Mag said:


> yeah, we use full strength but not exceeding 2ml per gallon with spot treatments.


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## Complexity (Jan 30, 2008)

2ml per gallon is the generally accepted rule for dosing H2O2. This is true no matter how you dose it -- squirting it directly on the algae (spot treatment) or dumping it into the tank (whole tank treatment). Either way, the H2O2 will end up being distributed all through the tank and filtration. The only real difference is the spot treatment targets the algae directly with a more concentrated dose (at the time of application -- it then spreads from there).

In either case, I would agree with Aquatic Mag's cautions regarding sensitive plants. I remember three plants that were known for melting: Vals, hornwort, and anacharis. I'm sure there are others, but the list is pretty short. Most plants can handle H2O2 just fine.

I have dosed as high as 4ml per gallon (I do not recommend that amount). I had no problems with it. The fish and inverts did fine as did the plants. I only mention this high dosage to reinforce that 2ml per gallon is a safe amount. I've even had shrimp (RCS and Amanos) jump into the exact spot where I'm spot treating (so they got hit with it directly) with no ill effects. They just swim off and act normal. No deaths. 

Edited to add that I prefer using an actual syringe to spot treat than a spray bottle. I think it would be hard to know how much you're dosing when using a spray bottle. I have something like these 4 x 10ml Syringe with blunt 4" Long Needle. The long needle makes it easy to spot treat with precision, and the syringe makes it easy to measure the proper dose for your tank.


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## alcimedes (Dec 7, 2014)

Complexity said:


> Then turn off the lights. Wait 15 minutes. Turn on the lights and filters.


The method you laid out sounds perfect, but killing the lights shouldn't be necessary.

Hydrogen peroxide does react with sunlight, but the lights over your tank for the time frames in question would be irrelevant.


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## Complexity (Jan 30, 2008)

alcimedes said:


> Hydrogen peroxide does react with sunlight, but the lights over your tank for the time frames in question would be irrelevant.


Thanks for that information. I never knew that. Is it UV light that breaks down the H2O2?


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## alcimedes (Dec 7, 2014)

Complexity said:


> Thanks for that information. I never knew that. Is it UV light that breaks down the H2O2?


Yes, and it's a process that takes weeks to months. You wouldn't want to store it in sunlight in a thin bottle for example, but you could put H2O2 in direct sunlight for an hour and likely not be able to measure a difference between an unexposed solution.


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