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How to winterise your pool correctly

When closing down your outdoor swimming pool for winter you need to create a sterile environment where microorganisms such as algae spores, fungi and bacteria cannot flourish. You also need to help prevent the formation of scale and staining from dissolved minerals so the water and pool surfaces are in good order when the pool is re-opened in spring.

If you can do this, you should hit the ground running at the start of next season as far as water quality is concerned, and avoid those expensive and time consuming clean-downs which are needed before the water begins to look acceptable again.

For Pools Run on Chlorine

First, shock dose the pool with an unstabilised granular chlorine. The high dose of chlorine will kill off any algae spores and bacteria that might be lurking in liner creases or in the surface of tile grouting. This will give you as near sterile water as possible. Now you need to keep it like this through the winter, as the chlorine will soon die away. You need to use a product that is specially formulated for overwintering and contains long life algicides and additives, which prevent the formation of scale and staining from dissolved minerals.

For Pools run on Bromine or Baquail

The above procedure and instructions opposite are aimed at pools run on chlorine, as it is by far the most commonly used outdoor pool sanitiser. There are parallel procedures for other disinfectants as follows.

Bromine is very similar to chlorine and can be shocked with shock dose. This should then be followed by the prescribed dose of winteriser product.


  1. Thoroughly backwash the filter. Remove any debris from the pump strainer, skimmers and pool water surface.
  2. Check the pH and adjust to 7.2 - 7.4.
  3. Shock dose with a stabiliser-free chlorine to kill any algae and harmful organisms that may be present. Allow the water to circulate for 3 - 4 hours to ensure thorough mixing.
  4. Close the valve/s from the skimmer/s and lower the water to 10cm - 15cm below the skimmer level. (It is important to heed any recommendations made by the pool installer and not lower the water level too much. This is especially important if there is a naturally high water table as this could present structural hazards to the pool shell).
  5. With the water still circulating through the bottom drain, add the winteriser product, pouring it evenly around the pool at the prescribed dose.
  6. Leave the circulation running for long enough to ensure thorough mixing.
  7. Remove ladders, diving boards and summer covers etc, and store them away from extremes of temperature.
  8. Switch off and isolate electricity supply. (If in doubt consult an electrician).
  9. Drain the water from the pump, heater and filter taking care to retain any ‘O’ rings from unions.
  10. Disconnect the pump and store in a frost-free, dry place away from extremes of temperature.
  11. Leave valves above water level open; those below should be closed and protected from frost damage.
  12. Some weighted and sealed polythene bottles can be used to absorb ice expansion. These should be floated along the length of the pool and secured with strong cord.
  13. Cover the pool with a heavy duty winter pool cover.
  14. Check the appearance of the water occasionally, along with the pH and free chlorine while the pool is shut down. If the winter is mild, add another dose of Winteriser in February and ensure thorough mixing and distribution throughout the pool.

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The Hot Tub and Swim Spa Company specialise in providing hot tubs, swim spas, pools and gazebos and have experience of over 50 years in this industry. We also offer servicing and post-sales care for all of our customers to make sure that our customers get the best out of their hot tub.