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How to clean algae off flagstone?

Posted by rooster99 (My Page) on
Wed, May 19, 10 at 22:46

With the mild winter here in Vancouver the algae is doing well on our flagstone deck and walkway - it's all green.

Can anyone recommend an effective, environmentally friendly way to get rid of the algae?

I can borrow a pressure washer but I'm concerned about damaging the grout between the flagstones. Our landscaper said he would replace whatever grout was damages, but I'd prefer not to have to go that route.

I've read of people using vinegar, but I've also read of that being used to kill weeds and I don't want to damage our gardens. I've read of something called BioWash, but I'm not sure of its effectiveness or if it's even available here in Canada as it's not on the Rona or Home Dept web sites and the web site is no longer available. I've read of people recommending hydrogen peroxide (3% solution) but that only seems partially effective. I've also read of oxygen bleach but I'm not sure what that is and am nervous about using any bleach near our gardens and with our dog in the yard.

Any thoughts?

TIA - R.

Follow-Up Postings:

RE: How to clean algae off flagstone?

Safer makes a moss and algae killer that should work well. I used it on my shed roof which was in the shade and had quite a lot of moss/algae on it.
Here is a link to a website that sells it. There is also a link on the site for MSDS info:


RE: How to clean algae off flagstone?

Did you find a satisfactory solution for removing algae from your flagstone. I have a similar problem with my Arizona Flagstone walkway in So-Cal (if you can imagine). I get conflicting information on the use of an acid wash but have not had luck with power washing or simple green products. Any suggestions?

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