Pool winterizing: active or passive, how to choose
When the water stays below 12 °C for good, it is time to winterize. Two methods: active winterizing, where filtration keeps running at low speed, and passive winterizing, where everything is stopped. The climate decides.
In short
You winterize when the water temperature drops durably below 12 °C: below that, biological activity is too low to justify normal filtration. Active winterizing (reduced filtration that keeps running) suits mild-winter regions; passive winterizing (full stop, anti-frost protection) is needed where it freezes hard. In both cases, the goal is to protect the installation from frost and to make the water easy to recover in spring.
Active or passive: the climate decides
Active winterizing keeps filtration running a few hours a day, which avoids stagnant water and simplifies restart; it suits regions where frost is rare. Passive winterizing fully stops the circuit, which is partially drained and protected with floats and anti-frost gizmos; it is the solution for harsh winters, where water in the pipes would freeze.
The common step: protect from frost
Whatever the method, the number-one risk is freezing of the pipes and equipment, which can crack them. You lower the water level below the skimmers in passive winterizing, fit anti-frost accessories, and cover the pool. Well-balanced water and a winterizing product limit deposits and algae during the cold season.
What to do, step by step
Wait for water below 12 °C
Winterizing too early, with still-warm water, encourages algae. Wait for the water to cool durably.
Clean and balance the water
Clean the pool and filter, adjust the pH, and run a shock treatment before closing.
Choose active or passive
Mild winters: reduced filtration (active). Freezing winters: full stop, partial drain and anti-frost (passive).
Add the winterizing product and cover
A winterizing product limits algae and deposits; a cover protects from debris and frost.
Frequently asked questions
At what temperature should I winterize?
When the water stays durably below 12 °C. Below that, micro-organisms are nearly inactive: normal filtration is no longer needed.
Should I drain the pool for winter?
No, definitely not fully: an empty pool can be damaged. You only lower the level below the skimmers in passive winterizing.
Active or passive, which is better?
Neither in absolute terms: it depends on the climate. Active for mild winters, passive where it freezes hard. Passive protects better from frost, active simplifies the restart.