We have several areas where algae builds up due to lack of direct sunlight and a cool/wet climate. We need to clean it off.

I don't want to pressure wash as last time it washed a lot of the grout/sand away from between the close fit flagstones. I shudder to think of the effect on the dry stack rock walls.

I'm nor afraid of adding elbow grease to the mix or having to do it every spring, but want something effective and friendly to both our garden and little dog. I've read suggestions of cider vinegar, TSP, and a potassium based soap that is sprayed on from Planet Natural. But nothing stands out and would prefer to minimize experimentation.

Any ideas?

TIA - R.