How to Winterize a Pool

Do you want to avoid green water, frost damage and extra work in spring? Then winterizing your pool is mainly a matter of timing and the right order in pool maintenance. Once the swimming season is over and the water has cooled sufficiently, you can protect the pool shell, the water quality and the equipment step by step.

This advice is mainly intended for permanent outdoor pools. For an above-ground pool, Intex, Bestway or hot tub, dismantling it and storing it where it will not freeze is often the safest choice, unless the manufacturer states otherwise.

When should you start preparing your pool for winter?

In most cases, you should only winterize your pool once the water temperature remains around 12°C (about 54°F) or lower. If you do it too early, algae and micro-organisms will still be active and you increase the risk of green water in spring. As long as the water is warmer, keep filtration and water treatment running as normal. In Belgium, the right time is often October or November, but the calendar is not what matters most - the water temperature is. A heated pool can stay in use later into the season, but even then it is best to wait until the water has genuinely cooled enough.

Active or passive winterizing?

There are two ways to keep a pool winterized. With active winterizing, the pool stays full and you keep the installation running on a limited basis. That requires a little more monitoring and energy, but the water usually stays in better condition and you can start up again more quickly in spring. With passive winterizing, you lower the water level, drain the lines and equipment, and shut the pool down. In our region, this is often the safest and most popular solution during longer freezing periods.

If you are still unsure about buying a pool, do not just look at shape and finish. Also ask how easily the pool, the cover and the pool equipment can be protected in winter. That also helps determine long-term ease of use.

Step-by-step guide for a permanent outdoor pool

1. Clean the pool shell, waterline and filter thoroughly

First remove leaves and other dirt from the water, then clean the floor, walls, steps and waterline. Also empty the skimmers and baskets. Give the pool filter one final service, for example by backwashing and checking the filter media. Dirt that you leave in place now will cling more quickly over winter and make spring start-up unnecessarily difficult.

2. Balance the water and add a winterizing product

Before closing the pool, check at least the pH and disinfectant level. A pH range of 7.2 to 7.6 is usually recommended. Correct the water balance and, if necessary, carry out a shock treatment that suits your system, such as chlorine or salt. Then let the filtration run long enough for everything to mix properly. Only after that should you add winterizing liquid according to the dosage on the label. This helps limit algae growth, limescale and stubborn contamination.

3. Now choose passive or active winterizing

With passive winterizing, you lower the water level below the return jets and other frost-sensitive built-in parts. Draining the pool all the way to the bottom is not a good idea, because the water also helps provide stability. With active winterizing, the water level stays normal and you maintain limited circulation. In that case, good freeze protection is important, especially when temperatures drop below freezing at night.

4. Winterize the pump, sand filter, pipework and heat pump

If you choose passive winterizing, switch off the installation, drain the pump, filter tank and pipework, and if necessary blow the lines dry. Fit winter plugs in the return jets and protect the skimmer with a Gizzmo skimmer plug. If you are winterizing your heat pump as well, make sure no residual water can freeze inside it. Disconnect loose, frost-sensitive parts and store them in a dry place according to the manual. If you have a saltwater pool, also check that the salt cell and sensors have been cleaned and stored correctly.

5. Protect the pool against ice pressure and cover it correctly

Use winter floats where needed to absorb the pressure of expanding ice, especially with passive winterizing. Then stretch a well-fitting winter cover or other suitable cover tightly over the pool. A proper cover keeps out leaves, rainwater and light, and helps keep the water quality more stable. During winter, check from time to time that the cover is still sitting properly and that the installation is still circulating correctly if you are using active winterizing.