Best way to clean the remaing Black stains off deck?? Potting Soil? or mold?

I have cleaned a deck and there remains what looks to be like potting soil and charcoal black stains on the deck .Might be black mold still? The rest of the deck looks fine but the black stains are not removing. My mix was 3-2% bleach with 32 oz of F-18 in 8gals mixed then applied straight . Any suggestions? Also.I did do a test spot of about 5% Bleach to see if that would help but didn't.
 

WASH-IT H.B.

New member
I don't know what sort of presentation you do when you are quoting a job but I always tell my customers " I can make it clean but I can't make it new." The black that you are looking to remove could have been there 15 years and is now well soaked in and an integral part of the makeup of the timbers. You will probably make it look worse stuffing around with Chem's trying to get out a stain that is deep within the fibres of the wood. leave it alone and be satisfied you have done for the customer the very best you could considering the deck was neglected for the last 10 years. It's a pressure washing wand you are using not a magic wand.
 
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