Dark streaks on white brick

Any idea how to remove these streaks? I tend to stay away from white washed brick like this, but the home owner was asking if there is anything I can do. I did a house wash on all the vinyl, his driveway, sidewalks and patio and he’s very happy. I made it clean from the beginning I would not be touching this brick and that was fine. I’d really like to see if I can go back and tackle this.

I’m really gun shy with white washed brick. Years ago when I first started doing this I pressure washed some and it took the white washing off. I’ve also cleaned a house with a white brick ledge around the bottom of the house that my normal house wash took off some of the white and made the brick appear more red.

The other guys can clarify, but looks like normal mildew/organics to me, so 3% and light rinse should take care of it. Just did a similar chimney yesterday.