How to Stop Algae

The most common alga site is a roof on which moisture is trapped and sun is not strong enough to dry it out.

Algae are common, simple plant forms that are found in moist, sunless areas. There are many different species, but the green and black algae are often found on the north sides of roofs and foundations. They really don't do much harm because there is little root structure to take hold and cause damage, but they are an unattractive addition to your house. Algae also can be found in fish tanks, landscape ponds and other water features. These algae are naturally occurring, and you can remove them mechanically with a skimmer and an algae scrubber. You cannot stop algae from forming in a natural water feature without resorting to chemicals that will kill the beneficial life.

Things You'll Need

• Pressure washer
• Hose
• Water
• Spray pump
• Oxygenated bleach or outdoor algae cleaner
• Long-handle scrub brush
• Ladder
• Copper strip
• Tin snips
• Small nails
• Pruners
• Saw
• Hammer

Instructions

1. Connect a pressure washer to your hose and spray away the algae that already exists. This will get the worst of the algae off the surface but will not eradicate them. The algae will reappear in a day or two if you don't conduct further treatment.

2. Fill a spray pump with 80 percent water and 20 percent oxygenated bleach. Oxygenated bleach is much more environmentally safe than chlorinated bleach, but it needs to remain on the area longer. Spray the algae-infested area and keep it wet for 45 minutes. Scrub the place two or three times during the waiting period to work the solution into cracks and crannies.

3. Rinse the area after the time has elapsed. The oxygenated solution is gentle and may need to be repeated if there is still evidence of algae. The solution will loosen any moss and lichen that have adhered to the surface, and it will clean dirt and grime, making the area clean and bright.

4. Prevent algae from recurring by installing a copper strip along the roofline or at the point where water is dripping. Interestingly, areas below metal stripping seem to be immune to algae growth. Unroll the copper strip and tack it down with nails. Cut it with tin snips at the end of the area.

5. Prune out limbs, where you can, to open up areas for sunlight to penetrate the area. Sun will kill algae and prevent themm from coming back better than any chemical. You do not need to mangle your trees, but remove some central tangle to enhance light penetration.

References

• RCI Online: Algae, the Growing Problem
• Ask the Builder: Removing Moss and Algae From Roofs