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Green algae? Reach for oxygen bleach — not chlorine bleach — and scrub away.

By Tim Carter,June 01, 2012

My house must be a magnet for algae. I have green algae on the shaded parts of my deck; it’s also on my patio and my vinyl siding. Furthermore, I believe there’s black mildew on my siding. Then there’s the roof. I have black streaks of algae up there. How can I safely remove the algae from all these surfaces without harming me, my pets or my plants? I’ve heard that bleach works, but something tells me that this is not the right approach.— Caroline B., Jackson, Miss.

You, I and millions of others suffer from algae around our homes. I have two decks, one on top of another. The lower deck has lots of shade, which is a perfect place for algae to grow. I also have algae coating stone steps on my property. I work at keeping them clean, because when they’re wet, the algae-covered steps are as slippery as wet ice.

The good news is that it’s not too hard to clean algae. The bad news is that there’s no silver bullet to inhibit its growth on all surfaces.

As far as bleach goes, there is more than one type. For many years, I thought bleach was bleach. When I was growing up, my mom used to buy those white plastic bottles of smelly chlorine bleach to use in our laundry. She would save the bottles, rinse them out and then fill them with water in case the water main broke outside our house. It was a big joke in our family, but my mom always was prepared!

Then, about 17 years ago, I learned about oxygen bleach. It does many of the same things chlorine bleach does, but it’s not toxic. Oxygen bleach is the preferred bleach to use for cleaning your home, both on the exterior and interior, because it will not harm you, your pets or your plants. Oxygen bleach also will not take the color out of your wood decking, your vinyl siding, your painted surfaces or your roof.

Chlorine bleach, on the other hand, is highly toxic to plants, humans and animals. It’s so powerful that it will remove the color from wood decking, and it can discolor painted exterior surfaces much like it takes out the color from fabrics.

You can easily find oxygen bleach online or at many stores. Typically, it is a powder you mix with water. Once the powder is mixed with water, all you get is more water, oxygen ions that do the cleaning and some harmless organic soda ash. Not all oxygen bleaches are the same. Some are completely organic, while others contain fragrances, dyes, color crystals and excessive fillers.

Last weekend, I mixed up some oxygen bleach to clean algae from my lower deck and from the deck railing. I simply dissolved the powder in warm water, poured it into a simple garden hand-pump sprayer and squirted it on the algae-coated surfaces. I allowed it to soak for about 10 minutes and then used a scrub brush to remove the green algae. After rinsing with a garden hose, the surfaces looked brand new!

You can clean roofs with oxygen bleach, but it can be challenging. The biggest problem is that it’s dangerous working up on a roof. The algae-covered roof, once wet with the oxygen bleach solution, can be very slippery.

It’s imperative that the roof surface, or any surface you’re cleaning, does not dry out before you get to scrub it. You must keep the surface wet with the solution at all times. This is hard to do on a roof on a sunny day, so it’s best to clean roofs on overcast days, when air and roof temperatures are cool.

You need to scrub the surface after the oxygen bleach solution soaks. Don’t ever think that you can just spray on any magical cleaner and get perfectly clean surfaces. Marketers that make that claim are appealing to your desire to take the easy way out. Don’t believe the spray-and-rinse claims for a second.

Tim Carter is a columnist for Tribune Media Services. He can be contacted through his Web site, askthebuilder.com.