Went and did the side of a two story with my 12v bandit and could not get it clean. The mix I used was basically 1 gal of 12% per five. I used 2 per 5 on the last job with my x-jet… Figured with no dilution this mix would be strong enough. It cleaned the whole house except where the chimney flashing was bleeding down the side. Obviously not mold like the rest of the house but there was still some black streaks as well as what looks like rust? Should I get some F9 on this? I think solution mix is part of the problem but no real pressure from the bandit to rinse that high. No more than hose pressure anyway.. This should have been an easy fix? What to do differently next time?