How to kill black bearded algae

Written by jamie conrad
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How to kill black bearded algae
A solution of bleach and water helps eliminate black bearded algae. (Thinkstock Images/Comstock/Getty Images)

Black beard, or black brush, algae is a type of red algae capable of living in both salt and fresh water. This type of algae is often black, deep purple or grey in colour, with short, brush-like hairs growing from its base. Black brush algae grows best on slow-growing plants, rocks or gravel in fish tanks and ponds as well as on solid surfaces such as the walls of tanks or ponds. Treat and remove black beared algae with special methods and tools.

Skill level:
Moderately Easy

Things you need

  • Bleach
  • Water
  • Algae-eating fish
  • Hydrogen peroxide
  • Syringe
  • CO2 tank or supplement

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  1. 1

    Treat the entire aquarium or pond, including fixtures, with a bleach solution. Do not expose your fish or live plants to this solution, however. Use this method only on new aquariums that have not yet been set up or on aquariums where fish and plants have been removed already. Combine 1 part bleach to 19 parts water. Place the aquarium and its fixtures into the solution or fill the pond with the solution if you are treating a pond. Allow them to sit in the solution for at least four minutes, then to dry completely.

  2. 2

    Add Siamese algae-eating fish or American flag fish to the aquarium or pond. These fish eat black bearded algae but do not eliminate algae completely because algae may live in the fish's digestive tract for several days. Algae-eating fish are merely an option to combat black bearded algae--not to completely eliminate it, according to the website Aquariums Life.

  3. 3

    Treat your tank or pond with hydrogen peroxide. Measure 1ml of hydrogen peroxide in a syringe for every 5 gallons of water. This method may be used with live fish and plants still in the tank. Keep in mind, however, that using too much hydrogen peroxide overdoses your tank or pond and can kill your fish. Again, this is merely an option to control the algae.

  4. 4

    Increase the levels of CO2 (carbon dioxide) in your tank or pond. Fish supply companies often sell filtration systems that add CO2 directly to the water as it filters through. You may also try allowing a CO2 tank to bubble directly into the water and use liquid CO2 supplements. Slowly increase the level of CO2 in your tank or pond to 30 parts per million, recommends the website AquaScaping World, as doing so too quickly may harm your fish. Keep the CO2 level in your tank stable thereafter, as fluctuating CO2 levels encourage algae growth.

Tips and warnings

  • Changing the water in your tank or pond less frequently helps maintain stable CO2 and nutrient levels, helping to reduce the growth of black bearded algae.

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