Rinse from the top of the roof down to avoid re staining the shingles with the dirty water.
How to remove stains off roof.
A mixture of trisodium phosphate tsp bleach and water will also remove stains.
Set the nozzle at the highest pressure setting and hold it 12 inches from the shingles.
If you decide to try it apply it shortly after you ve cleaned the roof.
Allow your roof ample time to dry off and then check on it.
Algae can be killed and the stains removed using chemical cleaners though they usually return over time.
Step 7 let dry.
Allow the mixture to sit on the shingles for 15 minutes then rinse the roof well with water from the garden hose.
Use a cleaner specially made for killing algae or by spraying a mixture of one part bleach to four parts water with tsp trisodium phosphate or other detergent added in a garden pump up sprayer.
If there are no more stains on the roof you re done.
Unless you are on scaffolding or a walkway near the roof you should wash the solution off from the ground.