Closing Your Pool for Winter: What Matters and What's Ritual
Updated September 2026
Quick answer: A good closing is 20% chemistry and 80% freeze protection. Balance the water, shock a few days before closing, add a winter algaecide if you like insurance — then do the part that actually prevents damage: lower the water below the skimmer, blow out and plug the lines, drain every piece of equipment, and cover tight. Close when the water is reliably below 65°F, not on a calendar date.
Chemistry for a long sleep
Final balance targets are the normal ones — pH 7.4–7.6, alkalinity 80–120 — with one twist: bring chlorine up with a routine shock 3–5 days before the cover goes on (not the same day, so the high chlorine doesn't sit against the cover and liner all winter). Cold water barely consumes chlorine, so the pool coasts on that dose for months.
Winter algaecide (a polyquat) is reasonable insurance in warmer climates and marginal in cold ones where the water stays under 50°F. Skip copper-based algaecides — the staining risk outlives the winter. 'Winterizing kits' bundle mostly optional products around the one non-negotiable ingredient: correct chemistry going in.
The freeze protection that pays the bills
Water expands 9% when it freezes, and that's the entire threat model: water trapped in pipes, pumps, filters and heaters cracks them. Lower the pool below the skimmer mouth, blow out the plumbing lines with a shop vac or compressor, plug the returns and skimmer (gizmos absorb ice expansion), and pull every drain plug on the pump, filter, heater and chlorinator. Store the plugs in the pump basket — spring-you will look there first.
In freeze country this section is the whole game: a $60 closing done right prevents the $600 cracked-pump spring and the $2,000 cracked-heater one. In mild climates that merely flirt with frost, running the pump on freeze nights is a legitimate alternative to a full blowout.
Cover and off-season habits
A tight cover is algae prevention, not decoration — sunlight plus organic debris is the recipe for a green opening. Safety covers anchor drum-tight; tarp-style covers need water bags or blocks (never bricks that can fall in) and a mid-winter check after storms.
The off-season isn't zero-maintenance: pump standing water off the cover occasionally, peek at the water level (a fast drop means a leak that's easier to fix now), and in warm snaps consider a quick chlorine top-up through a peeled-back corner. Ten minutes a month buys the easy opening.
FAQ
When should I close my pool?+
After water drops below 65°F and stays there — algae goes dormant, so a late closing beats an early one. Closing a warm pool in September is how you open a green one in April.
Should I drain my pool for winter?+
Never fully — an empty in-ground pool can pop out of the ground from groundwater pressure, and liners shrink. Lower it below the skimmer for a standard closing; that's as far as draining goes.
Do I need to blow out pool lines?+
In any climate with real freezes, yes — water freezing in pipes is the single most expensive winter failure. In mild-winter regions, running the pump during freeze events is an accepted alternative.