So, I’m essentially changing the physical texture of the concrete? I thought by using a pressure washer, I would just be removing any debris or stains. I started with a 25° nozzle, then went to 0°, which left the fine lines. I have a 15° nozzle somewhere I can use to make the surface look uniform. I’m not hurting the concrete by “blasting” it, am I?

You're not changing the texture of the concrete visible to us, although on the microscopic level its likely scouring the surface clean. The 15 degree nozzle keeps the pressure the highest while giving some width to blend the overlapping strokes. I like to do box sections, scanning the surface row by row similar to how a TV picture is scanned.

were you able to get rid of the marks . . . I just powerwashed front porch and now it looks terrible with dark marks

I was not. I resorted to covering them up wirh a large welcome mat.

Tim, may I ask what you tried? I was thinking of lightly sanding? Thanks so much for responding

I didn’t try anything other than hide it. Given that it removed some of the cement, the only thing I can think of as a fix would be to fill the areas with new cement.

It looks like you missed a few spots.