Lee, Im aware tht only low pressure should be used.. I was looking for advise on chemicals.. some say chlorine, some say other things.. since you jumped on this, Im guessing that you have some degree of expertise in this? What works best for you? Im new to this biz, but fortunatly not technicaly in th dark. Id be very careful about catching my runoff, and protecting the plants as well as any passersby. There are just so many choices out there I want to try to draw from the experience of other roof cleaners as to what is fastest, cost effective, safest, etc. but as always, Im looking for one word from my customer... WOW!