BLACK ALGAE



Black Algae will show up on pool surfaces as black rough spots. When you scratch a patch it should come off as a dark green colour.

  • Low levels of chlorine/bromine
  • High stabilizer level CYA (chlorine pool)
  • Poor water balance (high pH)
  • Poor or no circulation and filtration
  • High chlorine/bromine demand caused by:
  1. Dirty pool
  2. High bather load
  3. High temperatures (air and water)
  4. Heavy Rain
  5. Phosphates, Nitrates

Very stubborn algae to eliminate. The Outside layer will protect the inside layer. When you kill the outside layer it is important to brush off the dead algae to get at the protected under layer.


  1. For a chlorine pool test stabilizer (CYA) level. If CYA is less than 75 ppm proceed to next step. If CYA is greater than 75 ppm then follow “Dillution” formula to bring CYA below 75 ppm or add BROMINE PRE-TREAT at a rate of 400 gr per 10,000 litres of pool water (This will temporarily convert your chlorine pool to bromine so that CYA will not interfere with the algae treatment).
  2. Adjust water balance and pH to 7.0
  3. Brush all Black Algae spots. In a concrete pool use a stainless steel brush. In a vinyl or fiberglass pool use a stiff nylon brush.
  4. Put all pool tools (vacuum hose, vacuum head, vacuum pole, automatic pool cleaner, leaf skimmer etc) into the pool prior to and during superchlorination.

NOTE: Do not use service tools in a contaminated pool and then in a non contaminated pool. You will transfer the algae from one pool to another!

  1. Superchlorinate pool to 30 ppm (Follow chlorine chart for product choice, water volume and amount).
  2. Continue to brush Black Algae spots to remove protective outside layer.
  3. Maintain pool filtration and circulation system.
  4. Monitor chlorine/bromine level. If the level “zeros” out we may not have met demand. Repeat the superchlorination procedure to 30 ppm.
  5. Wait at least 24 hours and then add MBA-60 at a rate of 70 mls. per 10,000 litres of pool water.

NOTE: The longer that Black Algae has been attached to a surface the more difficult it will be to remove. It will also be difficult to remove from rough or porous surfaces. In extreme cases the pool may have to be drained and the algae physically scraped off.


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