What Causes Black Algae To Grow In Your Pool?

There are many different types of algae that one can find in a pool. Black Algae is the worst. Black Algae has the most resistance to chlorine and other chemicals than any other type of algae.

The reason for this is that the black algae have tiny tentacles that grip into the porous pores of a gunite and concrete pool.

You will also get black algae in fiberglass and vinyl pools as well. The only difference is that it is easier to clean the fiberglass and vinyl pools.


Black Algae are living organisms that have hard outer shells that grow and cling to porous pool surfaces. Black algae take the form of black or blue-green spots and can be clumped together with raised heads.

They do not float in the water. Black Algae do not brush off the pool walls easily either. They are the worst form of algae and the most difficult to get rid of.


Black algae can enter your pool in various ways.

  1. From people’s bodies. If they have been swimming in a river, dam, lake or the sea, just before swimming in the pool.
  2. From people’s clothes, if they were swimming in a river, dam, lake or the sea just before swimming in the pool.
  3. Any animal that gets into pools water can have the black algae on there fur or paws.
  4. Pool Accessories, pool equipment, can all carry black algae into the water if these things are not regularly hosed off with water or washed off with diluted bleach.
  5. Swimming clothing should always be washed before it is worn to swim.
  6. Black algae will form if the pool circulation system is not functioning correctly.
  7. Black Algae will form if the pool filtration system is clocked or has not been maintained therefore cannot remove contaminants out of the water.
  8. If the PH level of the pool water is too high.
  9. If the pool pump is not running for a long enough period. Recommended period 8 to 12 Hours a Day.
  10. When the pool pump is not running every day.
  11. When the amount of chlorine in the pool water is too low.

How to remove Black Algae is a hard job, unfortunately, somebody has to do it. You can save money by doing it your self with a bit of help from the family. You can read how I got rid of black algae in my pool.