5 Steps to Get Rid of Mustard Algae in Your Pool

Raise chlorine to shock level Mustard algae is tougher than green algae. A normal shock won’t kill it — you need to raise chlorine to shock level based on your pool’s CYA and hold it there for 48 hours.

Brush every surface daily Brush walls, floor, and steps at least once a day during the 48-hour shock treatment. The algae hides in crevices and needs physical disruption.

Keep chlorine high after treatment Don’t drop back to minimum chlorine levels. Keep it around 3–5 ppm depending on your stabilizer, and brush weekly to prevent regrowth.

Clean your filter more often Dead algae can hide in the filter and reinfect the water. Backwash or clean your filter more frequently during and after treatment.

Check for phosphates or nitrates If the algae keeps coming back, you may have a phosphate or nitrate problem. A phosphate remover can help, but the high chlorine plus brushing routine works for most people.