How to Remove Blue-Green Algae

Certain areas of the country, particularly those where the weather is very humid, are more prone than less-humid areas to blue-green algae (Gloeocapsa magma), which is spread through the air and shows up as stains on roofs. Although the algae is not harmful to the surfaces it comes into contact with, the stains it makes are not attractive. Removing them will require a little knowledge of what works and elbow grease.

Things You'll Need

  • Pump sprayer
  • Garden hose with attached sprayer
  • Gloves
  • Protective eyewear
  • Ladder
  • Coveralls
  • Non-slip shoes
  • Rope
  • ¼ cup trisodium phosphate (TSP)
  • 1 quart bleach containing 6% sodium hypochlorite
  • 1 gallon water
  • Stick or paint stirrer
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Instructions

  1. How to Remove Blue-Green Algae

    • 1

      Tie off your rope onto a fixed object, such as the chimney, to allow you to have a safety device before you climb on the roof. Make sure your ladder is in good shape and is well positioned. Having a helper to hold the ladder while you are climbing up and down is the best idea.

    • 2

      Mix the bleach, TSP and water, and put the mixture into your pump sprayer. Make sure the solution is well mixed by stirring it with a stick or paint stirrer.

    • 3

      Climb the ladder to the roof with the pump sprayer; hold onto the rope as you climb onto the roof. Spray the spots where the blue-green algae has formed. Soak the spots well and leave the solution on for 15 minutes.

    • 4

      Using the garden hose with attached sprayer, rinse the solution from the roof. The result will be a clean roof with no blue-green algae stains.