# warning about Hydrogen Peroxide



## Blacktetra (Mar 19, 2015)

I'm sure many know this, but it's never in bad taste to remind us:

what works once doesnt always work twice.

The effects of dosing H2O2 into a tank are more complicated than simply "it kills algae".
I've used a tank-wide dose of 1.5ml/us gal before with no casualties. This time around I'm having shrimp die. Why it worked previously, and now doesn't, I don't know. But dosing this amount of H2O2 into a tank that had only blood fin tetras and angel fish also killed the whole tank. There are likely reasons for it that I don't fully understand. Such as thread algae killed with H2O2 becomes toxic to shrimp. Or perhaps the blue green algae in the tetra/angel tank was in large enough amount that it's sudden death leached toxins into the water column.
Either way. When dosing any kind of chemical "solution" for your problems. Always do so realizing that tank chemistry isn't simple. What works in one tank may do horrible things in another.

Rest in peace tetras, angels, and shrimp.


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## Bushkill (Feb 15, 2012)

I'm gonna guess here too: If this was BGA or cyano that you were working on or any film algae in large enough quantities, the sudden die-off lowered available oxygen and/or as you suggested some alages are really bacteria that will take other organisms down with it.


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## goatnad (Aug 13, 2015)

First you should go with a lower dose. All though some people claim you can overdose peroxide by up to 3ml/g it's not needed. 1.5ml/g is still a bit much in my opinion. Try under 1ml/g. Also don't just pour it all in at once. Gradually add some over 5 or 10 mins. Doing a spot treatment on algae is a better thing to do. You'll use less peroxide and you add less peroxide to your tank making it a safer process. If you have algae that bad and have a reoccurring then you are not trying to actually find the root cause of it and solve it. Using peroxide is just a band aid.


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## auban (Jun 23, 2012)

Something to keep in mind...

Hydrogen peroxide works by oxidizing stuff. If there is a lot of organic solids in the water, it will oxidize them and dissipate relatively quickly. If it's practically straight RO water, then the only thing the hydrogen peroxide can oxidize would be the organic living things in the tank. That includes the plants, snails, fish, shrimp, etc.

So, the water itself makes a difference. Dirty water, go figure, seems to be safer with hydrogen peroxide than really clean water. Or at least safer with larger doses.


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## Blacktetra (Mar 19, 2015)

thank you all for your replies.
It's good to hear these things.

As for the assumption that I'm not solving the root cause of my algae problem, that is false. The cause of the algae problem is known. The tank is in a classroom where it gets light in a very bad spectrum for most plants, and it can't be helped that the light it gets, is from 7am to 5pm. Way too much photoperiod, and awful spectrum are a main cause. However this is a classroom "pet" and as such, it can't be kept in a closet where photoperiod/intensity/spectrum are far easier to maintain.

"just raise co2 and ferts to match it, that should help" I am aware, but I don't have $400 to drop into a CO2 system. And even if I did, this tank was never meant to be a "show" tank, it's just a "pet" for the classroom, one that gets blue green algae here and there, and needs to be treated for it once every few months.


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## Doppelgaenger (Jul 20, 2015)

vacuum your substrate, get all the mulm and uneaten food out. If this is a classroom tank I bet the kids are WAY overfeeding it. You do need to get rid of as much BGA as you can by vacuuming too.

You can't dose H2O2 into the water column and not expect issues. I spot dose H2O2 only, and only with the filter and all flow devices off. water and peroxide do not readily mix if there is no flow and you'll avoid exposing your fish and shrimp to them if you do it that way.

I've had shrimp walk across areas of substrate that were positively fizzing with bubbles from peroxide treatment and they never seemed to mind other than becoming bouyant from all the oxygen bubbles.


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## Blacktetra (Mar 19, 2015)

after reviewing, Auban, you were correct.
I'd been doing 30% changes once a week. Possibly even shortly before the whole-tank dose. There was nothing for the H2O2 to react with other than the algae and the fish. As a result, over 24 hours or so, it finally got the fish.


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## PlantedRich (Jul 21, 2010)

Any options like covering the tank back or a nice large poster placed to shield the tank from direct light? 
Wish you luck but a classroom tank is a bit of challenge.


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## Blacktetra (Mar 19, 2015)

It should help if the blinds in the room are closed each night to keep the sunset from shining in. I'll see if that can be arranged. Good idea.


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## mikeeOBS (Sep 22, 2015)

Just spot treated some GHA that were growing on my S. Repens. Saw it work and found some GHA growing on my HC and turned that treated area light brown. I'm sure someone has posted this already, but be careful if you spot treat HC with HP. Didn't realize how fragile those dudes are.


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## essabee (Oct 7, 2006)

I have had killing result from spot dosing with H2O2; and had promised myself never to try it again - and I haven't in the past 10 years or so, nor do I intend to use it ever in future.


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## dzega (Apr 22, 2013)

its not H2O2 that kills, its NO2 which arises after one wipes most of bacteria with peroxide.


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## seove (Aug 25, 2014)

The video that I saw warned against pouring H202 into the tank and instead said to use a spray bottle.

Bump: How long does it take to kill algae after spraying it?


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## concepts88 (Oct 4, 2012)

I spot dose in my 90 for about 8 years now, I never have any problems. I also overdose. (when I say overdose, I mean it. I go crazy) --
The entire tank, plants, and gravel is bubbling by the time I am done.

I have shrimp, plants, and it is an High tech tank with a lot of lightning. I never change teh water after dosing and I have super overdose before. Light breaks down the peroxide anyway, did you shut off your lights? Thats why it comes in that no see through brown bottle. What size is your tank. When in doubt, use less.. NEVER EVER had any fish or shrimp die. I also dose my Fluval Edge without any issues. I have good flow in my tank also with cannister filter and also some other powerheads.

I also dosed by "accident" Nearby fish like corys, and even shrimp, saes and they scatter away but they never die.

When in doubt, go with a lower amount. But if you are nervous, dont use it.

Bump:


seove said:


> The video that I saw warned against pouring H202 into the tank and instead said to use a spray bottle.
> 
> Bump: How long does it take to kill algae after spraying it?


Most algae will die almost immediately, The key is to KILL ALL CURRENT and FILTERS when you are dosing. NO current in the tank. Then I use a syringe I got from walgreens and does on top of the algae, it slowly falls down.

Some algae will turn pink immediately after a few minutes which means it is dead. 

Also, shrimp and other critters will go on the stuff you dose right after because it guess it softens the algae or whatever.

Bump:


seove said:


> The video that I saw warned against pouring H202 into the tank and instead said to use a spray bottle.
> 
> Bump: How long does it take to kill algae after spraying it?


This is not a medication or excel. You dont pour it in. You turn off all the current and DOSE on top ONLY the areas you want to treat.


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## sfshrimp (May 24, 2016)

You could try a twinstar...

https://www.aquascapeaddiction.com/articles/twinstar-nano-review-aquarium-algae-control-made-easy


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