Black algae requires brute force.

You need a copper-based algaecide and a stiff brush. Regular chlorine won’t cut it.

Black algae grows roots into the plaster or vinyl. That’s why it’s so stubborn. The surface may look clean after you brush, but the roots stay. You have to physically disrupt them.

Here’s the drill: Brush aggressively with a stainless steel or nylon brush (depending on your pool surface). Then hit it with a copper algaecide. Keep your chlorine high (superchlorinate) for a few days. Repeat the brushing daily. It might take a week.

Prevention is easier. Keep your chemistry balanced – especially chlorine and pH. Brush the walls weekly before algae gets a foothold. And if you see even a small black spot, attack it immediately.

Don’t let it take hold – once it does, it’s a fight.