Hello Everyone, My Name is Chad Pierce out of Nashville, NC. Chads's Pressure Washing, LLC. Been Washing for over 10 years. I have a house we just washed that I need some help on please. Darker blue siding which I knew I should have declinded but I did it anyways and it has came back and kicked me in the rear. Home is probally 2-3 years old. Washed house as usual and after it dired obviously there was some soap that has ran out of the air or weep holes in the vinly and left a white chalky residue. Seen this many times and just re washed and it went away. Not on this one. I have tried scrubbing with oxalic acid and still nothing. What am I missing here. Could the acid have been bad. It is some that was on the shelf for a few years that I used one time and it seemed like it was not count then. Any help greatly appericated. Thank you!!