Roof Runoff?

Need some help all…

Did this nasty nasty house and got it all clean but there is some roof run off that wont break for me.

Tried 50-50 mix down streaming, straight SH down streaming, added a few ounces of EBC in my mix as well and nothing worked. See where the chimney stack meets the peak for the stain.

Definitely looks like mold. Surprised your approach did not remove it. I could be also be rust if that chimney cap is rusting. I think if you have done your best pressure washing it then it is time to tell the homeowner it is permanent or try calling the siding manufacturer for suggestions.

Apex Pressure Washing