Scrub Away Debris
Carefully remove all excess debris from your rooftop. Clear away any of the larger debris such as leaves or other items that would get in the way of your cleaning. Your first priority should be to use a scrub brush to clear a small path to make it easier for you to safely maneuver on the rooftop without slipping. Use your scrub brush to remove the larger pieces of algae, but you do not have to try to scour away all of the algae just yet.
Next, you will want to create an oxygen bleach solution. Avoid chlorine bleach solutions, as these can discolor your roofing materials. Oxygen bleach is much more mild and is safe to use around humans, plants, and animals. Be sure to follow the instructions for mixing the oxygen bleach spray provided by the manufacturer as closely as possible.
Spray your oxygen bleach mixture over the entire algae covered area of your roof. Allow the mixture to settle into the algae for at least fifteen minutes. You should be able to see the algae begin to loosen and run off of the roof on its own. In order to completely remove all of the algae, you will need to use your scrub brush to loosen it.
The last step is to hose down the roof once the algae has been loosened significantly. The remaining algae should easily wash away, leaving your beautifully cleaned roof showing. If you have very heavy algae coverage on your roof, you may need to repeat the oxygen bleach, scrubbing, and rinsing process a few times until all of the plants have been completely removed. The algae cleaning process is much easier if you clean your roof fairly regularly.