"Black Algae" (actually blue-green algae) forms in cracks and crevices on pool surfaces, especially plaster finishes. We normally find black algae growing in, but not limited to, shady areas of the pool.

Black algae is more typically found in concrete or plaster finished pools; it is very uncommon to find it in vinyl liner pools. It is known for a heavy slime layer and "skeletal growths" that make it impervious to normal chlorine levels (1.0 - 2.5 ppm).  Black algae can grow "condominium style" providing layers of algae one on top of the other. Slight cracks in plaster or fiberglass walls are perfect breeding grounds for black algae especially when the pool is not properly maintained

As shown in the photograph, the water remains relatively clear.  However, almost all customers notice a high chlorine demand (use much more chlorine than normal). Black Algae can be mistaken for iron, manganese or cobalt staining (if it brushes away, it's algae).

If the treatment is not complete, the "roots" of the Black Algae will support the re-growth in the same spot.  Keep in mind that when the pool is shocked or heavily chlorinated, the "upper levels" of the algae will bleach out but the remainder of the condominium is protected from the chlorine attack.

Treatment:  

1. Have water properly analyzed. BALANCE THE POOL WATER. Proper pH, total alkalinity & calcium hardness are essential for the treatment to work.
2. Prior to and during treatment, the algae MUST be thoroughly brushed in order to "break open" the slime layer.  Failure to do this critical step will prevent the treatment from working. 
3. Pools treated with chlorine or bromine should aggressively shock with chlorine (Burn Out or Smart Shock) and use a good quality algicide such as Spot Kill, Back Up, Algae All 60 or Banish in extreme cases. 
4. Pools treated with SoftSwim or other Biguanides should top up their Bactericide level "B", add a double dose of algicide "A", and add a double dosage of shock or "C". 
5. Follow up either method with Optimizer Plus.

Prevention:

1. Maintain good, solid sanitizer levels all of the time.
2. Run the filter a minimum of 10 hours per day, everyday from opening to closing.
3. Vacuum the pool weekly.
4. Brush the pool walls & surfaces weekly (vacuuming doesn't count).
5. Shock the pool weekly.
6. Add algicide weekly.
7. Regularly clean solar blankets, ladders, pool toys, etc.
8. Use the pool.

Treating algae with Sodium Bromide.  Click here for all of our Algae treating products. 

Click here to purchase the chemicals mentioned in this article