Those homeowners or renters who have concrete walkways or paths know the frustration of persistent algae growth during the rainy season. With each rainstorm, a greenish-black growth starts to spread inch by inch. This organic growth can be dangerous if tracked into your home or car. It can be slippery and staining to your carpets, so make sure that you take steps to remove the stains before they become too hard to remove.
Assess whether the stain on your concrete is actually algae. If it is algae, the colour will be greenish-black and have a slick feel to the surface when you rub it with your finger.
Consider if you want to use chlorine or oxygenated bleach. Chlorine bleach can be harmful and toxic to your environment.
Visit your local hardware or home supply store and purchase the oxygenated bleach. It may be called "deck brightener."
Mix two parts of hot tap water to one part oxygenated bleach in your power washer.
Spray the concrete stained with algae. As you spray, you should see the algae peel away.
Let the concrete dry in the sunshine and repeat again if the stains have not disappeared.
Repeat spraying this mixture throughout the rainy season to prevent algae staining.
Rinse your patio or walkway after spraying with the bleach solution if you have small children or pets that may be walking barefoot on the walkway.
If bleach gets in your eyes, rinse with cool water immediately and go to the emergency room.