How to remove algae in an aquarium with hydrogen peroxide

Full Tank Dosing

  1. If you have moss balls, remove them (they are algae, and will die with this treatment).
  2. Turn off the filter. You may also remove the filter and put it in a bowl with aquarium water to maintain some beneficial bacteria.
  3. Start with 2-3 ml of 3% hydrogen peroxide per gallon of water, up to 4ml per gallon max. Note that this is per gallon of water, not the tank size, as the rocks, decor, fish, etc. can take up volume. You can also spot treat up to maximum dosage by turning off the filter.
  4. Wait for about an hour or two.
  5. Reinstall and turn on the filter.
  6. Test the water for ammonia/nitrate spikes during the week, as the algae and micro-organisms dying may cause spikes.
  7. Do a partial water change a couple of days later.

Notes on Full Tank Dosing

  • After dosing the tank with hydrogen peroxide, it is important to change the water. This is due to the fact that a lot of organisms were destroyed during the process, and the organic matter will begin decaying. If a water change hasn’t occurred, the decaying organic matter will again cause an algae bloom.
  • Dosing the tank with hydrogen peroxide should be the last resort, as it will risk restarting the nitrogen cycle. This may cause ammonia, nitrite, and nitrate spikes and must be closely monitored if the aquarium contains living animals. Plants are less affected and might benefit from this instead, as plants can readily take up ammonia, nitrite, or nitrate.

Plant Dip Method

Take the plants out and dip them into hydrogen peroxide 3% at full strength to as little as 1 part per 10 parts water. Leave the plant in solution for a maximum of five minutes. Try to avoid roots, unless the roots are also covered in algae (for plants that don’t have normally buried roots).


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