It’s not all over, but we have a number of spots in different areas on the bottom. And one of the curved walls looks yellow. But we aren’t really seeing rust, so maybe it’s not metals. I tried an algaecide, but not specifically for mustard algae. And there is an area on the liner above the water line (see photo). Do you think it’s probably mustard algae?

I appreciate the help. I know it’s tough to diagnose via photo!