I did a dryvit house the other day with tons of redclay and green crap all over it. It took most of it out. I've talk to other pressure washers around me and they swear by bleach. I talked to one that said he had a house that wouldn't come clean. He tried every chemical he had and the only thing that worked was bleach.
I have to say I'm loyal to bleach. And the 1 time I tried to "broaden my horizon" I got screwed. The owner of this PW store told me this certain chemical would clean brick. So I paid $50 (Which is all I had in the bank). I tried it and it didn't work. I diluted it at first which he said you could do. Then I tried putting the pickup striaght into the chemical. Still no results. Then I dumped it on the side of a house straight up and it didn't do a thing. So I've become weary of using anything else. I don't have the money to be tryin stuff out just to learn that someone was just trying to sell me something.
I use bleach on everything. Until bleach doesn't work it is what I'll use. I was just suggesting because I've seen people who will use anything but bleach then end up going back to it later on.
Also I have a coldwater system. I think a lot of those chemicals require Hotwater to work well. I wasn't sure of what he was using. But I felt it was worth mentioning.