Peroxide Treatment For Algae in Aquariums

Treatment with hydrogen peroxide For Algae in Aquariums

Blue Green Algae can be from green to almost black

Many aquascapers have resorted to using hydrogen peroxide to treat problem algae when all else fails. Here we provide dose rates, procedures, and precautions for treatment. This treatment is controversial when reviewing sources on the internet. What we can tell you is we have used it both in tanks with plants and fish and aquariums with shrimp without harm most of the time. Over dosing is not recommended. Peroxide has been used for years in aquaculture for emergency oxygen replenishment. Here is an article by a veterinarian at the University of Georgia who works with fish. In addition, this is a source for aquaculture treatments that have been tested with peroxide in higher concentrations.

Before using H2O2 hydrogen peroxide treatments against algae In order to get answers to basic questions about algae in the aquarium, we recommend you read this article first and this article about Fighting Algae. If your aquarium is infested with stubborn green algae, for example, or blue-green algae, treating the entire tank with hydrogen peroxide (H2O2) or spot treating is a solution we have resorted to from time to time. Such a treatment should always be considered the last resort, and it should only be applied when the standard methods have failed and you’re about to just give up on your aquarium because you cannot get rid of the algae. Use a dosage as high as necessary and as low as possible in order to spare the animals in your tank undue stress. Certain plants like Riccardia sp. (coral moss) or Riccia fluitans (liverwort) may be damaged in the course of this treatment. Some other aquatic plants may turn a lighter color temporarily, but this is not necessarily a sign that the plant is dead.


As a basis for this treatment, we use the 3% of hydrogen peroxide. Do not exceed the percentage of H2O2-of 3% or you may have a hard time calculating the dosages correctly. Depending on the algae species, we recommend different dosages:

Here is a video of me testing this on a tank with BB Puffers ( Coming Soon)

  • In the case of blue-green algae: Use 1.5 to a maximum of 2.5 ml of the 3% solution of hydrogen peroxide per gallon of water.
  • In the case of green algae: 20.25 ml to a maximum of 32.5 ml of the 3% solution of hydrogen peroxide per 13 gallons of water.
  • Shrimp or delicate species To kill stubborn patches of algae (BBA, Cladophora), one can use HYDROGEN PEROXIDE (3% concentration), using an eye-dropper tool (see below) to spot dose directly onto algae. Be careful not to exceed 1ml per gallon for delicate for livestock.

The amount of hydrogen peroxide above is added to the algae-infested tank three to four days in a row. Try to spread the solution as evenly as possible, ideally areas with a good current to avoid local overdosing. 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 normal and no reason to worry. These bubbles consist of pure oxygen, they are harmless. Do not dose for more than three to four days. Many species like blue-green algae respond quite fast to this treatment. Others species may need a few days until they die off. The green algae start losing their color and turn lighter and lighter. When the treatment is finished, change at least 50% of the aquarium water. As we cannot totally rule out that beneficial bacteria are compromised by hydrogen peroxide we recommend adding an efficient bacteria starter after the water change to help the beneficial bacteria Activate to repopulate your tank quickly.


In extreme cases you can combine hydrogen peroxide with Evoke. The two solutions must not be mixed; use them separately. When adding Evoke use the maximum dosage recommended by the manufacturer DIRECTIONS: One teaspoon (5 ml) of EVOKE treats 25 gallons (100 L). Do not exceed this dosage and add only one dose per day. Observe plant reaction and adjust dosage as necessary. The simultaneous use of H2O2 and Evoke has the advantage that the oxygen depletion that may be caused by Evoke is more than leveled out by the oxygen produced by the hydrogen peroxide. The combined use of both products increases their effectiveness considerably.


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 (goggles, gloves). Use at your own risk! We do not assume any responsibility for damages that may result from this treatment.