Hydrogen Peroxide

Hydrogen Peroxide *** The information contained here is subject to frequent changes as I experiment and learn more about the usefulness of H2O2 ***

What It Treats – Provides temporary relief for Marine Velvet Disease and Brooklynella. After a 30 minute H2O2 bath, the fish should be transferred into a Quarantine Tank (QT) and treated with either copper or Chloroquine phosphate.

How To Treat – The following is needed:

1. 3% Hydrogen Peroxide (USP grade) – available at most drugstores or Walmart
2. Large glass bowl or container (Food grade plastic bucket is fine as well)
3. Syringe or pipette (for measuring out the H2O2) and measuring cup (for adding saltwater to the glass bowl)
4. Metal spoon for mixing

1. Prepare saltwater for the bath by having it set to the right temperature and heavily aerating it. You can accomplish the latter by running an airstone or pointing a powerhead towards the surface of the water for at least 1 hour (longer is better). Alternatively, you can use Display Tank (DT) water or even from your Quarantine Tank (QT) provided no medications/chemicals are present in the water.

2. Add saltwater (using measuring cup) to the large glass bowl. Keep track of exactly how much water is added – either in cups or ml. (Do this beforehand if preparing saltwater for the bath right in the glass bowl.) Make sure your fish has enough water to swim around.

3. Using a syringe or pipette, add 3% Hydrogen Peroxide as per dosing instructions below. After dosing is complete, stir the water using a metal spoon. You can also use an airstone to provide oxygen during the bath and help mix the peroxide into the water.

Dosing instructions: To achieve ~ 150 ppm H2O2 add:

  • 1.25 ml of 3% H2O2 per 1 cup of saltwater.


  • 5 ml of 3% H2O2 per 1 liter of saltwater.


  • 20 ml of 3% H2O2 per 1 gallon of saltwater.
4. Now it’s time to add the fish. It’s okay to use a heater, but probably not necessary since the bath only lasts 30 minutes. Observe closely and remove the fish if showing signs of distress. The vast majority of fish will handle it just fine. After 30 minutes, remove the fish and transfer into a QT for further treatment: https://humble.fish/velvet/

Pros – Effective, easy-to-source “pre-treatment” before fish is placed in QT with copper or Chloroquine. In this study, a single 30 minute treatment with 75 ppm hydrogen peroxide “greatly reduced” Velvet trophonts on the fish: https://www.researchgate.net/publication/230234979_The_Application_of_Hydrogen_Peroxide_as_a_Treatment_for_the_Ectoparasite_Amyloodinium_ocellatum_Brown_1931_on_the_Pacific_Threadfin_Polydactylus_sexfilis

Cons/Side Effects – Still experimental so side effects are not really known. It’s possible some fish may not tolerate this treatment. (Check the Fish + peroxide compatibility list before using.) Avoid using H2O2 on fish with an open wound or obvious infection. Although H2O2 is an antiseptic, it has been found to slow the healing process and possibly worsen scarring by killing the healthy cells surrounding a cut.

*** Further reading on use of Hydrogen Peroxide for fish:

*** At this time H2O2 is only appropriate to use for the following scenarios:

  1. Hybrid Tank Transfer Method: Hybrid TTM to treat all parasites!
  2. For temporary relief of velvet & brook. It can also be used as temporary relief for uronema; however the H2O2 will aggravate the red sores if a fish has an active infection.
  3. Bath treatment prior to entering quarantine. The fish may or may not require further treatment in QT. Best to observe for 30 days with black mollies alongside: Black Molly Quarantine

To be clear, I do not expect the above to be the “final say” on using H2O2. But research and experimentation into this new treatment is going to take time. What I’m trying to discourage is people taking liberties with the treatment, and just dropping the fish in their DT straight away after one 30 minute bath. Best to at least observe in QT (with no meds) for 30 days before doing that.