How to Get Rid of Black Algae in Your Pool


Green algae can turn crystal clear water into jungle soup almost overnight. It’s a nuisance, but with regular pool care, it’s easy to control. Getting rid of black algae, however, is much more challenging. Get ready for a workout.

What is Black Algae?

Algae is a group of marine organisms with the characteristics of both plants and animals. Thousands of species live and reproduce in water, using sunlight and organic material for food.

Black, or black-beard algae, is classified as cyanobacteria — bacteria-like organisms capable of photosynthesis. In addition to green chlorophyll, it contains dark pigments that give it a distinctive deep blue-green to black color.

Is Black Algae Harmful to Health?

Black algae alone is not generally harmful to humans or pets unless swallowed, but like most algae, it produces a thick slime that encourages the growth of dangerous, disease-causing bacteria such as E. coli. Swimmers should stay out of a swimming pool with black algae until it’s treated.

Recognizing Black Algae

Black algae looks like mold. It first appears as dark spots on pool walls where it will grow into beard-like clumps if left unchecked. Unlike species that float in water, black algae form roots that adhere to the walls of plaster and concrete pools, making it impossible for chemicals alone to remove it. Black algae is rare in vinyl-lined and fiberglass pools because of their smooth surfaces.

Getting Rid of Black Algae

Black algae doesn’t go down without a fight — it takes large volumes of chemicals and plenty of elbow grease — but you’ll be swimming again in no time by following these six steps.


  1. Test the pool water and balance it for alkalinity, pH and chlorine levels. It makes chemical treatment more effective.


  1. Clean the filter — rinse cartridge or backwash sand or DE filters thoroughly. Use a chemical filter cleaner for heavily infested pools.


  1. Brush the pool vigorously. The mechanical force breaks down the surface coating that protects black algae from chemicals. Edges and corners above the water’s surface can be cleaned with a hand brush or the edge of a chlorine tablet.


  1. Shock the pool with a quadruple treatment of sodium hypochlorite shock at dusk and let the pump run overnight. Soak brushes in the shallow end of the swimming pool to sanitize them.
  1. Vacuum the pool floor and repeat steps 2-4 until the algae is gone.


  1. Retest and balance your pool water, adding chlorine and your regular algaecide treatment.

Preventing Black Algae

It’s much harder to get rid of black algae than to prevent it, so be vigilant by:

  • Checking for algae daily and treating it promptly
  • Maintaining your pool regularly
  • Showering before swimming and washing suits and toys before using them in your pool

Final Thoughts

Why struggle to get rid of black or green algae when it can be prevented with regular maintenance? Swimming pools can be both fun and hassle-free with quality pool care from Marine Blue Pool Service.