I have to go through this process at least 2 times a year. I mix outdoor bleach with a car wash. The Bleach gets the algae and the car wash gets the dirt and other materials. The sheeting action of the carwash helps the water and bleach to come off the windows and house like it was waxed. Works for me. Rinse with lots of water to dilute the bleach on the ground. Cover plants with roll plastic.