How to Treat and Prevent Excessive Chlorine Loss


WHAT IS IT?

The consistent inability to maintain chlorine levels is also called “chlorine demand” and is most often caused by a high level of contaminants in the water. Those contaminants force the chlorine to work extremely hard to oxidise them, leaving little chlorine to protect swimmers. Proper chlorine levels cannot be re-established without first eliminating the contaminants. External factors such as sunlight and heat also contribute to chlorine loss.

WHAT ARE THESE CONTAMINANTS?

  • Human Outputs: Sweat, urine, saliva, and skin cells.
  • Personal Care Products: Sunscreen, tanning oils, makeup, hairspray, and deodorants. (These create the “grease line” at the tile mark).
  • Algae & Bacteria: Green, mustard, and black algae, as well as water-borne pathogens like E. coli.
  • Nature’s Debris: Dust, leaves, grass clippings, flower petals, and “tree droppings.
  • Insects: Ants, beetles, and the “pool-favourite” drowned crickets or frogs.
  • Bird Droppings: A major source of phosphates and pathogens (microscopic “bad guys”—living organisms like bacteria, viruses, and protozoa that cause illness in humans).
  • Fertilisers: Nitrogen and Phosphates that blow in from the garden or wash in during a thunderstorm.
test your pool water regularly

HOW TO TREAT EXCESSIVE CHLORINE LOSS

  1. Check pH first: If pH is above 7.8, chlorine is only 20% effective. Drop it to 7.2 – 7.6.
  2. Test Stabiliser (CYA): The ideal stabiliser level is between 40-80 ppm. Without “sunblock” for your water, the sun destroys your chlorine.
  3. Run the pump and filter: Run the pump and filter for at least 8-10 hours, ensuring the water is moving while the sun is up.
  4. Apply a Shock Treatment: Add 200g Month Mate Granular Xtra Blue per 10,000L or 2 x Bags Month Mate Shock Xtra Blue per 50,000L to destroy contaminants.
  5. Test the free chlorine level every 12 hours. If the free chlorine level is below 1ppm, repeat the shock treatment.

NOTE:

  • A ‘chlorine demand’ fix is often not a quick fix and could require a significant amount of granular chlorine to be applied over a 24 – 48 hour period before a Free Available Chlorine reading is registered.
  • It is, though, crucial that a Free Available Chlorine reading is achieved between 1 – 3ppm, and that it holds within this range over a few days.
  • Normal weekly shock treatment can only then resume to maintain it between 1 – 3ppm.

HOW TO PREVENT EXCESSIVE CHLORINE LOSS

  • Maintain ideal chlorine levels (1-3ppm).
  • Apply the Month Mate Super Plus Floater.
  • Backwash and rinse the filter when necessary, usually once a week.
  • Keep the weir and pump baskets clean and remove leaves, insects and debris from the pool before they start to decompose.
  • Maintain proper water balance, test and adjust pH weekly and Total Alkalinity as needed.
  • Shock routinely, apply Month Mate Shock Xtra Blue, 1 bag per 50 000L once a week.
  • Run the pump at least 8-10 hours per day in summer and 6-8 hours in winter.
  • Chemically clean the filter at least twice a year, at the start of the swimming season and then again before winter starts.