Used cobbs acid on areas as well as his powermax. Powermax was the clear winner though. I did scrub one area to see if it was really needed. Used a 175 with a nilogrit brush.
When I went to the next area, I couldn't see a difference, so I just went the "chem and dwell route".
There was some staining though. Dark areas that wouldn't even budge when I used a wire brush by hand. No biggie though, I have done this one in the past and they know the drill.
As far as the business end of the hose......I used the turbo hybrid at 1200 psi.