What is the best winterization for a swimming pool?

Why winterize your pool?

In winter, swimming stops, but the water and equipment remain exposed. A properly carried out winterization pursues three objectives:

• Protect the equipment and structure from frost: pipes, pump, filter, skimmers and jets can suffer when water freezes inside.
• Preserve the water quality to avoid a laborious reopening in spring.
• Limit the deposits of leaves, dust and limescale on the walls.

A persistent misconception is to empty the pool for the winter. This is generally to be avoided: water supports the structure and the liner. An empty pool can deform, and a liner can shrink or peel off. Always follow the recommendations of your pool manufacturer.

Active or passive winterization: the differences

Active winterization

The filtration continues to work, but for a reduced duration. The water remains in motion, which limits the risks of frost in the pipes during cold periods, and allows you to keep an eye on the water quality. We continue to regularly check the pH and adjust the treatment.

Its advantages: better maintained water and a quick restart. Its constraints: higher electricity consumption and regular monitoring, including during frost episodes, where the filtration may need to run more.

Passive winterization

The filtration is stopped for the whole winter. We lower the water level below the skimmers and return jets, we purge the pipes and equipment, and we place winterization plugs in the orifices. The pool is then covered.

Its advantages: no operating cost and little monitoring. Its constraints: a more careful preparation, and water that generally requires more work in spring.

How to choose?

A few questions guide you:

• Are frosts frequent and lasting in your area? If so, passive winterization is often safer.
• Can you monitor the pool throughout the winter? Active winterization requires regular checks.
• Is your equipment room frost-free? If not, carefully purge the pump and filter.
• Do you want to reopen the pool early in spring? Active winterization facilitates a quick restart.

If you are still hesitating, nothing prevents you from combining: an active winterization at the beginning of the cold season, then switching to passive winterization if a lasting frost episode is expected, provided you purge and plug the circuits at that time.

The time to start winterization depends on the water temperature. In practice, we start it in autumn, when the water cools down permanently and swimming is over.

The steps to a successful winterization

1. Clean the pool: vacuum the bottom, brush the walls and the waterline, empty the baskets.
2. Balance the water: adjust the pH then the disinfectant. A shock treatment before winterization is a common practice; follow the dosage on the label.
3. Clean the filter by backwashing, or clean the cartridge.
4. Add the winterizing product according to the label and the volume of your pool, filtration running to distribute it well.
5. In passive winterization, lower the level, purge the circuits and equipment, and place the winterization plugs.
6. Cover the pool with a well-stretched winter cover.

Useful products and accessories

The CTX WinterStar Power winterizing product is a concentrate that helps maintain the water in good conditions during the winter period and limits the formation of limescale deposits. Its sheet indicates that it does not foam, does not contain copper and does not stain liner, reinforced PVC or polyester coatings. Indicated dosage: 0.5 L for 40 to 50 m³, or up to 100 m³ with a one-liter bottle.

Adapting winterization to your pool type

The main principles remain the same, but each type of pool has its points of attention:

• Pool with liner: do not lower the water level too much, as the liner could shrink. Lower it just enough to pass below the skimmers and jets.
• Polyester shell: the shell needs the weight of the water to stay stable against the pressure of the ground. Never empty it without the manufacturer's advice, and monitor the waterline, where limescale deposits readily attach.
• Masonry pool: it withstands variations better, but the pipes and parts to seal remain sensitive to frost.
• Above-ground pool: depending on the model, the manufacturer recommends either winterization in water, or disassembly. Follow its manual, and protect especially the fittings and the filtration unit.

Preparing for reopening now

A careful winterization is already half of the reopening. Before closing the pool for the winter, a few precautions will save you time in spring:

• Store the disassembled parts (baskets, drain plugs, pressure gauge) in the same container, dry, with a label.
• Write down the last pH and disinfectant values measured before winterization.
• Take a photo of the valves and their position, to put the installation back in service without hesitation.
• Make a list of products and parts to renew, to order them before the return of good weather.

During the winter

Even in passive winterization, take a look at the pool from time to time:

• remove the leaves and the rainwater accumulated on the cover;
• check that the water level remains below the skimmers in passive winterization;
• in active winterization, check the pH and adapt the filtration during frost episodes;
• check that the plugs are still in place after a frost episode.

Errors to avoid

• Winterizing dirty or unbalanced water: the problems worsen during the winter.
• Completely emptying the pool without manufacturer recommendation.
• Forgetting to purge the pump, the filter and the pipes in passive winterization.
• Letting the cover load with water and leaves all winter.
• Overdosing the winterizing product thinking it protects the water better.

In spring, a well winterized pool restarts in a few days. Our article on cleaning a pool after winter accompanies you for this step.

Frequently asked questions

Is active or passive winterization better?

Active winterization is suitable for mild winters and for those who can monitor the pool. Passive winterization is safer when frosts are frequent, provided you purge and plug the circuits.

Should you empty your pool for the winter?

Generally no: water supports the structure and the liner. Always follow the recommendations of your pool manufacturer.

What dose of winterizing product to use?

For CTX WinterStar Power, the sheet indicates 0.5 L for 40 to 50 m³, or up to 100 m³ with a one-liter bottle. For another product, follow its label.

When to start winterization?

In autumn, when swimming is over and the water cools down permanently.

What are winterization plugs for?

They seal the pipes after purging, in passive winterization, to prevent water from returning and freezing.

Should you continue to monitor the pool during the winter?

Yes, even in passive winterization. Remove the leaves and the accumulated water on the cover, check the water level and the hold of the plugs, especially after a frost episode or heavy rain.

Also read

• How to clean an above-ground pool after winter?
• How to choose a sand filter for a pool?
• How to set up your pool equipment room?