Yellow stains are probably iron. Try ascorbic acid.
I don't know where sand is coming from.
If you have dust that's brown to yellow, it's probably mustard algae. Do a full SLAM.
Do you have a good, close up picture of the sand?
I don't know where sand is coming from.
If you have dust that's brown to yellow, it's probably mustard algae. Do a full SLAM.
Do you have a good, close up picture of the sand?