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Hydrogen Peroxide for Algae Removal

Hydrogen Peroxide for Algae Removal


Hydrogen Peroxide can be used safely and effectively for a partial fix to algae outbreaks.


There is no real OVERALL cure for algae outbreaks without hitting the real source of the problem, but the use of Peroxide can really help combat some of the larger outbreaks that new tank owners might encounter as they learn the ropes of fish keeping with out the need for tearing down their tank.

So, if your aquarium is infested with stubborn green algae, blue-green algae, beard algae or some slime right out of ghost busters, we highly recommend you treating the entire tank with hydrogen peroxide (H2O2) and not copper or other harsh chemicals or heavy metals.

Hydrogen Peroxides chemical is pretty safe and the makeup seen at an elemental level is “H2O2” When it breaks down it coverts to “H20” and “O” (Water and a single molecular of Oxygen) which is 100% safer than the Copper method of removing algae and is not poisonous to livestock.



Algae’s cellular structure is much like Bacteria is… and everyone knows that peroxide is a pretty good and cheap antibiotic, with that mentioned you now know how it can kill algae in your tank.


You need to always keep in mind that using such a treatment should always be considered you last resort, and you should only apply it when the standard methods like less food, more water changes and some basic maintenance of the tank on a regular time frame did not work.  You could also use it when all other methods have failed and you’re about to just give up on your aquarium because you cannot get rid of the algae or slime.

You need to always use a dosage as high as necessary and as low as possible in order to spare the plants and animals in your tank any undue stress or possible death. Certain plants like Riccardia sp. or Riccia fluitans have been said to be damaged with the use of H2O2 treatment. During treatment some aquatic plants may turn a lighter color just temporarily, but this is not necessarily a sign that the plant is dead and most will recover just fin and even grow better later.


As a basis for this treatment, we like to use the 3% max solution for the H2O2 in 1 gal = 3.785 L . You need to make absolutely 100% sure you do not exceed the percentage of H2O2-of 3%  because if you do you may have a hard time calculating the dosages correctly with my direction.

Depending on the algae species that is making you nuts, there are different recommend dosages I use that are pretty much safe and tested:


For blue-green algae: The safe range – 1-3 mL of the 3% solution of hydrogen peroxide per 1 gallon or 3.785411784 liters.


For green algae or slime or beard algae: 4-6mL of the 3% solution of hydrogen peroxide per 1 gallon or 3.785411784 liters this is a max dose treatment and if your fish shows signs of stress be ready to do a 50% water change.


In order for you to calculate the correct dosage you need for your aquarium, simply multiply the tank volume by the dose needed or use the software at the bottom of the page.

Example: 20 gallon tank with blue green algae would use 3ml max per 1 gallon or 3.785411784 liters. 20gx3ml=60ml


How to Proceed
You should apply the H2O2 to your tank before you turn off the lights at night, because the peroxide breaks down much faster in light. Also if it is possible to lower your filtration flow rate or cut off your filters for the night shortly after adding the peroxide (this gives it some time to mix through your water first and not removed)

I can not stress enough to keep in mind the higher the dose the higher the likelihood, some of the more sensitive fish like tetra or scaleless fish in your tank may die. Start with lower doses first and work your way up after you know for sure the lower dose is not enough because the Algae is still alive after a few days (would be still a normal color).

Blue Green Algae – Will show some bubbles and then disappears after a day or 2
Beard Algae – Will turn a reddish after 1 day and after a few more days starts turning white and into fish food.
Strand Algae – Will turn from the brownish color to bright red/orange and then to white in about the same time frame as the Beard Algae and a day or 2 longer than blue-green.

The amount of hydrogen peroxide 3% stock that you have found out in the calculation above is added to the algae-infested tank three to four days in a row. When you add the H2O2 kinda try to spread the solution as evenly as possible across the whole tank and just do not dump it in. You should ideally add it to areas with a good current to avoid any fish getting a full face full and overdosing.

Please think and make sure you do not hit any plants or animals directly with the solution. You will notice many tiny bubbles that form in your tank after the addition of hydrogen peroxide – this is totally normal and no reason for you to worry. These bubbles consist of pure oxygen, they are harmless and in fact a great side effect of this treatment.


After a few days have elapsed during treatment, you should give your aquarium some time to rest. Especially true if blue-green algae respond quite fast to this treatment, but for green algae may need some extra days until they die off. Then the green algae start losing their color and turn lighter and lighter. When the treatment is finished, change at least 50% to 75% of the aquarium water.


I can not stress this enough especially to new fish keepers, you should never combine hydrogen peroxide with any other treatments ever. Of course, there will be “someone” who says it is “OK”; please use them separately. When adding treatment, keep to the maximum dosage recommended above. If necessary, increase the dosage slowly and only in small steps (to a maximum of 6 ml per gallon or 3.785411784 liters). The simultaneous use of H2O2 and any other treatment could cause oxygen depletion and considerably stress you fish.


Helpful Info
A liter is defined as one cubic decimeter (1 L = 1 cubic dm). Hence 1 L = 0.001 cubic m.
1 gallon (gal) = 3.785411784 liters (L) = 231 cubic inches = 4 qt = 128 fl oz.
U.S. liquid gallon is defined as 231 cubic inches and is equal to 3.785411784 liters or about 0.13368 cubic feet.
Determining the amount of water in your aquarium is as simple as knowing that volume equals length times width times height and that 1 cubic inch of water is equivalent to 0.004329 gallons. Therefore, the volume of your tank in gallons of water = length x width x height (measured in inches) x 0.004329.
Here is a handy site for conversions.


NOTE: Dosing Directions Minimum to Maximum
This is the safe range – 1-3 mL per gallon or 3.785411784 liters and the MAX range not so safe is 4-6 ml per gallon or 3.785411784 liters.


Aquarium Gallons Calculator


I need to add this in here because I am not at your home working with you. I do not know what you have added to your tank or how well you follow directions.
Please read the safety instructions of each product before use. Avoid direct contact with skin, eyes and clothing, as well as direct contact with animals or aquatic plants. We recommend the use of protective gear when working with any chemicals (goggles, gloves). Use at your own risk! We do not assume any responsibility for damages that may result from this treatment or any other for that mater.
Following this method incorrectly can and does pose risk to your fish. Understand that adding anything to your tank you take that risk!



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