5 Steps to Kill Black Algae in a Pool

Brush with a stiff wire brush Black algae has a waxy protective layer that normal chlorine can’t penetrate. Use a stiff wire brush, not nylon, to break that coating.

Shock with triple the normal chlorine Raise chlorine levels to three times the usual amount. Lower pH to 7.2 and keep the pump running continuously.

Apply a pool algaecide Use a standard algaecide after shocking. For stubborn cases, try a copper-based algaecide, but avoid overuse—copper stains pool surfaces.

Repeat brushing daily for a week Brush the affected areas every day for seven days. This prevents the algae from re-establishing its protective layer.

Prevent with consistent maintenance Keep chlorine levels steady, brush the pool weekly, and run the pump long enough to fully circulate the water. Black algae thrives on neglect.