Mustard algae vs green algae: Mustard algae is a war of attrition, green algae is a cleanup job

Green algae floats, turns water cloudy, and usually responds to a single shock treatment. Mustard algae clings to walls like yellow-green dust, brushes off easily but comes back within hours, and laughs at normal chlorine levels. The fix for mustard requires brushing everything, shocking at 2–3x normal dose, running the filter 24/7, and brushing daily for a week — plus a mustard-specific algaecide if it reappears.