Another vote for wet and forget. It isn’t instant. Give it a week, the result will surprise you.

I thought bleach & simple green would get it done - worked, but algae came back quicker than expected. Jomax lasts 1-2 years on white siding on the N side of the house that is shaded constantly.

Used Jomax. Worked fairly well with one gallon's worth, but I may need to mix up some more for some spots that were really covered with moss and lichen too.