Banging Out The Black Algae: 3 Natural Options For Removing Black Algae Off Your Roof

5 February 2015
 Categories: Construction & Contractors, Articles


As a homeowner, you are most likely familiar with the tasks necessary to uphold value and appeal. Unfortunately, no matter how much emphasis you place on cleaning your home's exterior, some issues are inevitable. If you live in a humid climate, you may develop a discoloration on your roofing shingles. This discoloration may be black or a dark green, but will appear in streaks or blotches across your roof.  Black algae, or Gloeocapsa magma, is the most common cause of this discoloration on roofs. With this guide, you will have a better understanding of black algae and learn the safest methods of removal.

Black Algae Facts

While surprising to hear, the black algae is not truly black in color. In most cases, it appears as a dark, greenish discoloration against asphalt shingles. For most homeowners, the black algae is not terribly unattractive, but it can damage your shingles if left on your roof.  Fortunately, removing the algae is possible.

Natural Cleaners

At the first sign of discoloration on your roof, you may reach for traditional bleach. While bleach is an effective and efficient option for removing mold, mildew, and this dreaded black algae, it can also kill surrounding landscaping. When cleaning your roof with a power washer, the excess bleach will run off onto grass, shrubs, trees, and flowers around your house. In addition, chlorinated bleach can be hazardous to your own health. Even while working outdoors, you may experience the following health issues when using bleach:

  • Eye irritation
  • Skin irritation
  • Coughing, wheezing, and other respiratory issues

Thankfully, there are natural options to remove the black algae and clean your roof.

Hydrogen Peroxide

In an outdoor pump sprayer, add the following ingredients:

  • 4 gallons of water
  • 4 cups of hydrogen peroxide

Shake the sprayer container to mix the ingredients before pumping the handle to create pressure. Spray a thorough amount of the solution onto patches of algae and let sit for 30 minutes. Use a pressure washer or your garden hose to rinse off the roof. The hydrogen peroxide safely kills algae growth, but also removes dirt from your roof.

White Vinegar

Vinegar contains naturally antibacterial and antiviral properties, so it is a great ingredient to have for eco-friendly cleaning. To use white vinegar on your black algae, add the following to your outdoor pump sprayer:

  • 4 gallons of water
  • 3 gallons of white vinegar

Shake the container to mix before dousing the patches of black algae. Since vinegar is a natural ingredient, allow sufficient time for it to soak into the algae. After spraying, let it rest for about an hour. Then, rinse with your power washer or garden hose.

Oxygen Bleach

If the solutions made with hydrogen peroxide and vinegar are not effective, a more involved cleanser may be necessary. Fortunately, oxygen bleach offers the strength of bleach without the toxicity that will harm your health and home's landscaping.

To use oxygen bleach on your roof, complete the following steps:

  1. Fill an outdoor pump sprayer with 4 gallons of water.
  2. Add 4 cups of powdered oxygen bleach to the container.
  3. Shake the container to mix. Be sure the powdered bleach dissolves into the water.
  4. Pump the handle to create pressure before dousing patches of black algae.
  5. Allow the solution to soak for 20 minutes.
  6. If necessary, use a soft-bristled brush to scrub tough areas of algae.
  7. Use a light-duty pressure washer that offers 2,000 PSI, or Pounds per Square Inch, or water pressure to rinse off your roof. Be sure to hold the nozzle a few inches away from the shingles to prevent damage.

Maintaining your home's appeal is important for its value. However, removing black algae is imperative for the health of your roofing shingles. Using these natural options, or by calling a professional at a site like, you will remove the algae in a safe, effective way.