How do I fix Black Spot?

What is Black Spot?

Black Spot is the appearance of black spots (surprise, surprise!) on the surface of your pool. There are several types of algae that cause Black Spot. You will know it is Black Spot because it is very difficult to remove them with standard brushing.

Why does Black Spot occur?

Black Spot is the result of a contaminant entering your pool and, poor circulation or not enough Chlorine.  The contaminant can be anything that blows in off the wind, dropped by a bird or vegetation that falls in. During really hot weather and intense sunlight, Black Spot can take hold within a couple of days.

How can I prevent Black Spot?

The most efficient way to prevent Black Spot is with sensor-based Chlorination that responds to the changing conditions of your pool. Pooled Energy’s Pool Automation has two in-built solutions for preventing Black Spot:

  1. The automation controls the operation of your Chlorinator in response to changing weather, seasons, time of day and pool chemistry.
  2. Our Advanced Water Chemistry (AWC) typically maintains a more stable pH environment that effectively sanitises the pool and creates a beautiful swimming environment.

As with all pool maintenance routines, the basics apply to Black Spot prevention:

  • Keep the skimmers and filters clean to ensure flow is maintained.
  • Backwash every 4-6 weeks.
  • Maintain salt levels in salt Chlorinators. Usually 4,000-6,000 ppm depending on the Chlorinator.
  • Maintain Chlorine levels in freshwater pools. Liquid Chlorine deteriorates with time, so fresh is best.
  • Ensure the Chlorinator operates at appropriate times and for sufficient periods. During summer this means 8-10 hours per day at night when the sun won’t deteriorate the Chlorine immediately. During winter it can be reduced to 4-5 hours.
  • Maintain the pH level.

How do I remove Black Spot?

Black Spot can be hard to get rid of without the help of muscle and chemicals.

  1. Brush the algae first to remove its protective coating.
  2. Use hydrochloric acid to lower the pool pH to 7.2-7.4.
  3. Add 2 litres of liquid chlorine per 10,000 litres of pool water.
  4. For black spot on the floor of the pool, sprinkle with calcium hypochlorite.
  5. Run pool filtration for 24 hours.
  6. Do not swim for 24 hours, or until chlorine levels return to normal.

Good luck!


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