Winterising your pool: active or passive, and how to get it right
- Two schools: active winterising (filtration keeps running at low speed) and passive (full pool shutdown).
- The choice depends on climate: frequent, lasting frost → passive; mild winters → active, simpler and better for the water.
- The golden timing rule: winterise when the water drops below ~12 °C for good — not before.
- Winterising done right at the right moment = a spring reopening ten times easier.
Winterising is the art of putting your pool to sleep without it taking revenge in spring. Two schools: active winterising — the filtration keeps ticking over, the water stays visible and monitored — and passive winterising — level lowered, pipes drained, cover on, fully asleep. The right choice mostly depends on your climate (rare frost → active; serious frost or a second home → passive). And the variable everyone gets wrong is the timing: you winterise when the water drops below ~12 °C for good, not on the first free weekend in October. The CliniPool app tracks YOUR pool’s temperature and tells you when the moment has come.
Active or passive: choosing in 30 seconds
Active winterising keeps the circuit full: filtration a few hours a day (the bare minimum — in cold weather the water asks for almost nothing), an anti-frost controller that forces it on through freezing hours, and a glance at the water every two to three weeks. Advantages: simplicity, no draining, water that stays in good shape and a trivial reopening. Conditions: a climate where frost stays occasional, and a minimal presence on site.
Passive winterising cuts everything: lower the level, drain pipes and equipment (the deadly enemy is water freezing inside the circuit), fit floats and accessories, treat, cover. Advantages: zero worries all winter, resistance to severe frost, ideal for long absences. The cost: the full procedure in autumn, and a more substantial reopening in spring.
Timing, the number one factor
Winterising water at 18 °C means sealing biologically active water under a cover: the algae will work all autumn and you’ll find a pond in April. Below a lasting ~12 °C, aquatic life slows to a crawl and the water “holds” all winter. The same logic applies in reverse come spring: wake the pool before the water climbs back above 12 °C — otherwise the race against the algae starts without you.
The steps that really matter
The step-by-step guide above covers the full passive procedure. If you only remember three things: clean, balanced water before the cover goes on (you put a healthy pool to sleep — you don’t sweep a problem under the rug), pipes genuinely drained in frost zones (burst pipework is THE winterising claim), and an opaque, taut cover (light feeds algae, even in cold water).
With active winterising, the essentials come down to two settings: a short filtration time matched to cold water, and the anti-frost protection. The app handles both — its filtration calculation follows the temperature continuously, winter included.
And in spring?
A well-run winterising is judged in April: clear or barely hazy water, back up and running in half a day. The pool opening guide (“Also worth reading”) takes over from there — including for the rough awakenings: its “brown water” scenario is covered by the app.
Frequently asked questions
When should you winterise your pool?
When the water drops below about 12 °C for good: below that, algae and bacteria are practically dormant. Winterising too early (water still warm) lets biology keep working under the cover — the recipe for green water in spring.
Active or passive winterising — how do I choose?
Regions where frost is rare and brief: active (short daily filtration, water checked from time to time) — it's simpler and the water stays in good shape. Frequent, lasting frost, or a second home: passive (level lowered, pipes drained, floats, cover).
Do you need a winterising product?
It's a plus with passive winterising: it limits algae and limescale over the months without treatment. It's no magic wand — it complements a clean, balanced, properly closed pool; it won't rescue water that's already turned.
What if the pool freezes during active winterising?
The critical point is still water in the pipework. With active winterising, you run the filtration through the freezing hours (moving water freezes far less easily) — that's the job of anti-frost controllers.