Easily Remove Algae with Hydrogen Peroxide

Manually removing algae is usually a tedious process and it is really difficult to get every last bit. Let me share with you an easy method that uses Hydrogen Peroxide (H2O2) to get the rest of the harder-to-remove algae.

Before you begin, remember that removing algae is not the same as solving your algae issues. To solve your recurring algae issues, you need to tackle the root causes and that is another matter altogether. This method helps you remove the existing algae while you try to tackle the root causes.

Important Things to Remember:

  • Get the right concentration of H2O2. In most pharmacies, you can get 3% H2O2. It is also possible to get stronger ones from some gardening and hydroponics supply stores and even stronger ones from chemical/laboratory supply stores. You can still use those; just remember to handle these with even more care and adjust the dosage proportionally.
  • Be careful handling H2O2. Certainly, keep it away from young children. 3% H2O2 is used in healthcare to clean wounds and for many other purposes. In most cases, they need to be diluted before use. Even just a drop of 3% H2O2 on your skin may result in a tiny “burn”. It isn’t painful, but you’ll see a mark that will go away in a few days. In general, do NOT inhale it (mist or aerosol), drink it or let it get in the eyes. For 3% H2O2, handle it like you would handle household bleach. For the stronger ones, the precautions are similar to a controlled-lab kind of safe handling.
  • Don’t let H2O2 get to your filter bio-media. It will also kill most of the beneficial bacteria. But this can be easily avoided. This will handled in some of the steps below.
  • Once opened, H2O2 doesn’t have a long shelf life, roughly 6 months. And the efficacy drops with each passing week. So don’t bother buying big bottles for economic long-term use. If the store offers bulk discounts, get many small bottles instead. However, I do not recommend this as a long term regular treatment.

Which Algae it Works On

This method will work with most algae except Green Dust Algae and Green Spot Algae. It definitely works with Black Beard Algae, Hair Algae, Thread Algae, other similar algae and Blue Green Algae.

Removing Algae with Hydrogen Peroxide

Let’s begin:

  1. Manually remove as much alga as easily can.
  2. Turn off all filters. This is to prevent H2O2 from getting into the bio-media and killing the beneficial bacteria. Remove any internal filters (like sponge filters) and place them in a container with tank water.
  3. If you depend on the beneficial bacteria in your substrate, on the rocks, etc., they will likely be killed as well. Get a beneficial bacteria product for dosing after the treatment.
  4. If you have a small pump, add it to the tank to create some gentle circulation. If you don’t have one, that’s fine.
  5. Dose 50ml of 3%H2O2 for every 100l (25 US gallons) of tank water. Spread the dose over different parts of the tank surface.
    • Precaution: do not pour it directly on top of any fish, shrimp, etc. It’s fine when it is diluted by your tank water, but that initial concentrated pour on top of any small fish or shrimp could be fatally overwhelming. Optionally, mix the dose in a container of tank water and pour that water in immediately.
    • If you get the stronger concentrations, just do a simple conversion. For example, if you get the 20% one: 20% is about 6.6x stronger (20% / 3% = 6.6), so you dose 6.6x less. So instead of 50ml per 100l, you should dose about 7.5ml per 100l (50ml / 6.6 = 7.57ml).
  6. If you do not have a small pump mentioned earlier, just use your hands to gently swirl the water around for a while to spread the dose throughout the tank.
  7. Wait for about 1 hour. As the H2O2 works on the algae, you may see a lot of fine bubbles. These are Oxygen (O2) bubbles. H2O2 will break down into H2O (water) and O2 in that hour. Technically, it can be over in as soon as 30 minutes, but we wait 1 hour just in case.
  8. Perform a water change if you wish, but it is completely unnecessary as H2O2 only leaves behind H2O and O2.
  9. Turn on your filters and dose beneficial bacteria products if you need/want to.

The treatment is done. The algae might not seem the worse for wear, but over the next few days, up to a week, the algae will slowly die and get eaten and/or disintegrate. Again, this does not solve the root cause. It is simply an easy way to remove existing algae. If you do not treat the root causes, the algae will grow back within a week or two.

I hope that helps and good luck in your battle against algae. If you find this article helpful, do share it with your friends or community.

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