I'll be eager to see the other suggestions, but I use bleach too. It doesn't take much though so I dilute it at about a 10:1 ratio. No measuring is involved, just 'guess pouring'. Then I spray it on the patio when I first notice the mildew.

I don't think chlorine has much residual, especially in sunlight, so it's not really likely that one application lasted for years. Something else probably changed. Maybe when the HOA did the cleaning it washed mold spores off the building and they settled on your patio where they started to thrive.

Kate

I use bleach also. Actually, I have spent the last 2 days cleaning the aluminum structure for my screened patio. With all the rain we've had, the mildew was so bad I had to hand wash most of it. Chlorine evaporates within 24 hours, if I remember correctly.

I don't think there's much to clean mold but chlorine. TSP is supposed to work, but I don't find it very effective.

If you get all the mold off, and you use a penetarting concrete stain to seal the concrete it won't happen again or at least for several years till it needs the stain again. They call it stain but it looks like paint and comes in colors. We did our driveway and side walk 8 years ago and it is just now showing some spots. H&C concrete stain can be purchased at HD and Lowes. ;o)

Thanks, everyone. Darn. I've got a nice little ecosystem out there and I hate to do anything that might be even moderately toxic to the snakes, land crabs, etc.

If you use a hand held spray bottle you shouldn't disrupt the surrounding area. Living creatures will just stay away from the patio until the chlorine breaks down; I'm pretty sure that bodiggly is right and it's gone within 24 hours. After spraying I've never seen dead snakes or even anoles. Chlorine is a natural and abundant chemical. We didn't creat it and used in moderation it's not going to destroy the habitats in your yard. It's good to be concerned and careful, but I don't think you need to worry.

Thanks for the encouragement, solstice98.