How To Winterise An Outdoor Swimming Pool

Winter Debris Cover on Swimming PoolThat familiar time of year has once again arrived for outdoor swimming pool owners, preparing to winterise the pool and close it down until next spring.

It may not be the most fun task of pool ownership, but correctly winterising your pool will protect your swimming pool equipment and minimise the chance of algae growth while the pool is closed (because nobody wants to start next Spring off by clearing a green pool, right?).

Let us make the process a bit easier for you in this simple step-by-step guide on how to winterise an outdoor swimming pool (run on chlorine).

Winterising an Outdoor Chlorine Swimming Pool

Step One:

Backwash your sand filter thoroughly. Remove any debris from the pump strainer, the skimmer and the pool water surface.

Pool Filter on Backwash SettingStep Two:

Check the pH and if necessary adjust the level to between 7.6 – 7.8 using All Swim Pak 2.

The reason for this is that while the pool water is stagnant while closed, the pH will naturally lower, so raising it prior to winterising helps to avoid any negative effects from low pH on the pool surface or on the liner such as staining. 

Step Three:

Using an un-stabilised form of chlorine, shock dose the pool at a rate of 70g shock chlorine per 1,000 gallons (pre-dissolve in warm water and leave the circulation on to make sure it is thoroughly distributed).

Shock dosing is necessary to ensure you kill off any algae or harmful organisms in the pool.

Step Four:

Close the valve(s) from the skimmer(s) and lower the water to around 15cm below the skimmer level. This is to prevent the pool water overflowing in high rainfall levels.

Next, close the valve for the skimmer on the plant room filter, to prevent air suction via the skimmer.

Test and Treat Pool Water Test StripsStep Five:

With the water still circulating through the bottom drain, add a winterising product such as All Swim Winterclear, Lo Chlor Winteriser, or Lo-Chlor Total Algaecide

These are specially formulated long-life algaecides, designed to help prevent the formation and growth of algae for up to a 6-month time period.

Please note that if the winter season is particularly mild and wet, it’s advisable to check the water after 3 months and add another shock chlorine dose if needed.

Step Six:

If you have a pool ladder or diving board, remove them at this stage and safely package them away in a frost-free location for winter, along with your summer pool cover.

Step Seven:

Switch off and isolate the electricity supply. We recommend contacting a qualified electrician to carry out this process if you are in any doubt or unsure at all.

All Swim Pak 2Step Eight:

Drain the water from the filter, the circulation pump and the heater (taking care to retain any o'rings from the unions).

Step Nine:

Disconnect your pool pump and safely store it somewhere free from extreme temperatures.

Step Ten:

Leave the valves above the water level open, and close off the valves below the water level to protect them from frost damage.

Step Eleven:

If you choose to, you can now insert some weighted and sealed polythene bottles, floated along the pool length and secured with strong cord. The purpose of this is to absorb ice expansion in the event of harsh winter weather.

Step Twelve:

Winter Debris Cover on Swimming PoolCover the pool with a good quality Winter Debris Cover to keep your pool free from debris and leaves (and unwanted wildlife!). If the winter is particularly mild and damp, we recommend checking the water after 3 months and if necessary topping up the shock chlorine and another dose of algaecide. 

And there you have the complete guide to ‘putting the swimming pool to bed’ for winter, safe in the knowledge you are looking after the equipment and less likely to face a pea-green sight next spring!

If in doubt, we recommend contacting a local swimming pool engineer, as this is a service they will more than likely offer and be highly experienced in the process. 

All Swim can put you in contact with South Wales based pool engineers if required. Please call 02920 705059 or email for more information.

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