Mustard algae is a different beast.

Look for yellow-green dust that brushes off easily but comes right back within hours. Green algae floats, turns water cloudy, and usually responds to a single shock treatment. Mustard algae clings to walls and floor like powdered pollen, and it laughs at normal chlorine levels.

The fix is not complicated, but it requires patience. Brush everything — walls, floor, ladder, steps. Then shock the pool with enough chlorine to reach breakpoint (usually 2–3x normal shock dose). Run the filter 24/7 and brush every day for a week. If the yellow dust reappears after the first round, hit it with a mustard-specific algaecide and repeat the shock.

Green algae is a cleanup job. Mustard algae is a war of attrition.