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How to Kill Black Algae in Aquariums

Updated April 17, 2017

Algae are plantlike organisms that live mostly in water. Black algae grows well in aquatic environments rich in sunlight and nutrients. So naturally, aquariums are attractive environments for black algae. While some algae can indicate a healthy aquarium, it can appear unattractive, has the tendency to take over an aquarium and may be difficult to get rid of. Fortunately, there are certain measures you can take to help prevent the growth of algae.

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  1. Use your hands and an algae scraper to remove as much of the algae as you can. Manually removing algae is the safest method for getting it out of your tank. Using algae scrapers will not imbalance your water quality or disturb your fish.

  2. Cover your aquarium with a black trash bag for a few days. This will prevent sunlight for getting into the tank. Since algae require regular sunlight to live, removing sunlight will kill the black algae in your tank. However, this method is not recommended if you also have other living plants in your tank as they may die as well. If you can, remove the other living plants and place them in a separate aquarium. An alternative method is to relocate your aquarium to an area of your house away from windows and direct sunlight. Remove the bulbs in your aquarium and let the aquarium sit in low-level light.

  3. Change the water in your aquarium. Do not change all of your water at the same time as this will likely kill your fish and any other living plants in the tank. Start by changing 20 per cent of the water in your tank every day. Keep doing this until you get rid of the algae. Then, continue to change 20 per cent of the water in your tank at least once a week. This will limit the amount of nutrients in your aquarium, thus limiting the nutrients needed by algae to survive.

  4. Introduce algae-eating fish to your aquarium. Plecostomus catfish and Siamese algae eaters are two algae-eating fish that do a great job of keeping algae off your plants, rocks and glass. Both fish are non-aggressive so they shouldn't disturb your other fish.

  5. Tip

    Avoid using chemicals to kill the algae in your aquarium as chemicals can be harmful to your fish and plants.

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Things You'll Need

  • Algae scraper
  • Black plastic trash bag, if needed
  • Extra aquarium for live plants, if needed
  • Siphon, hose and bucket
  • Plecostomus catfish, or Siamese algae eating fish

About the Author

Baptist Johnson was first published in 2000 when a poem he wrote won first prize in a local writing contest. He also writes and edits for Etched Press Society, a micro-publishing company based in Wilmington, N.C. Johnson has a Bachelor of Science in business administration from East Carolina University.

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