How to Close a Pool for Winter: The Full Closing Checklist
Closing a pool for winter means balancing the water first (alkalinity, pH, calcium), shocking it 2 to 3 days before the cover goes on, adding a stain and scale preventer, then a winterizing algaecide right at the end. After the chemistry is set: lower the water level, blow out the plumbing, add pool antifreeze, plug every fitting, and install the cover.
Skip a step or do them out of order and the water sits under a cover all winter fighting itself. A pool closed green, or closed with chlorine and algaecide dumped in on the same afternoon, usually opens green too, because the algaecide got neutralized before it had a chance to work.
When is the right time to close a pool?
Once overnight water temperatures hold at or below 65°F for several days in a row, algae growth slows enough that closing is safe; full dormancy doesn’t happen until the water drops closer to 40°F (Pool Research). Closing earlier, in warmer water, is a common reason a “closed” pool turns green by December: the algaecide and shock go in, but the water is still warm enough for algae to keep growing underneath the cover.
If a hard freeze is forecast before the water has cooled to that range, close anyway rather than risk burst plumbing. A slightly early close costs a little more chemical; a burst pipe costs a repair bill.
What’s the correct order for closing chemicals?
Closing chemistry runs in the opposite order from opening: balance the water first, then sanitize, then protect it for the winter. Start several days to a week before the actual close so there’s time to retest between each step.
- Alkalinity, then pH, then calcium hardness. Target 80 to 120 ppm alkalinity, pH 7.2 to 7.6, and calcium hardness 175 to 275 ppm depending on whether the pool is vinyl, fiberglass, or plaster (In The Swim, pool closing chemicals).
- Shock, 2 to 3 days before closing. Let the free chlorine reading fall back to 1 to 3 ppm before doing anything else; closing a pool with a hot chlorine reading wastes sanitizer and can fade a vinyl liner over the winter.
- Stain and scale preventer, about a day before closing. This needs at least 8 hours of circulation to distribute evenly, so add it with the pump still running, not as the last step before the cover goes on.
- Winterizing algaecide, last, right before the cover. Never add algaecide on the same day as a fresh shock treatment. A high chlorine residual deactivates algaecide before it can do its job, a common reason a “properly closed” pool still opens green in spring (In The Swim, pool closing chemicals).
What does the physical shutdown involve?
Once the chemistry is set, the equipment side comes next, and it’s mostly about getting water and air out of anything that could freeze and crack.
- Lower the water level below the skimmer and returns so freezing water in the lines has room to expand without cracking the plumbing.
- Blow out the plumbing with a shop vac or air compressor, running at a low pressure (around 30 psi is the standard trade recommendation) to clear the lines without stressing fittings and joints (Royal Swimming Pools, blowing out pool lines).
- Add pool antifreeze, propylene glycol only, never automotive antifreeze, to any line that can’t be fully drained. Dosing runs roughly 1 gallon per 10 feet of pipe; a typical residential inground pool needs 4 to 8 gallons total.
- Plug every skimmer, return, and equipment line with winterizing plugs or gizmos rated for freeze expansion.
- Drain the pump, filter, heater, and chlorinator, and store any removable equipment (ladders, cleaners, solar covers) indoors.
- Install the winter cover, pulling it tight enough that debris and standing water can’t pool in the center.
the printable pool closing checklist
- Confirm water temperature has held at or below 65°F for several days
- Balance alkalinity (80 to 120 ppm), then pH (7.2 to 7.6), then calcium hardness
- Shock the pool 2 to 3 days before closing; let free chlorine fall to 1 to 3 ppm
- Add stain and scale preventer with at least 8 hours of circulation
- Add winterizing algaecide last, never on the same day as shock
- Lower water level below the skimmer and returns
- Blow out the plumbing (roughly 30 psi) and add pool antifreeze
- Plug skimmers, returns, and equipment lines
- Drain pump, filter, heater, and chlorinator; store removable equipment
- Install and secure the winter cover
What does professional closing cost versus doing it yourself?
| Approach | Typical cost | What’s included |
|---|---|---|
| Professional, inground pool | $200 to $500 (commonly $300 to $350) | Labor, standard closing chemicals, blowout, cover install |
| Professional, above ground pool | $150 to $300 (commonly around $175) | Labor, chemicals, cover install |
| DIY, chemicals only | $30 to $70 | Balancing, shock, stain preventer, algaecide |
| DIY, antifreeze | $10 to $30 | Propylene glycol for exposed plumbing |
| DIY, plugs and gizmos | $20 to $60 | Winterizing plugs for skimmers and returns |
| DIY, pre-packaged closing kit | $30 to $80 | Chemicals bundled for a standard-size pool |
(Ranges compiled from Angi’s pool closing cost data and HomeGuide’s pool closing cost guide, 2026.)
How far do you actually lower the water?
It depends on the cover type, and the trade doesn’t agree on one exact number, so treat this as a range rather than a fixed measurement. A solid cover generally sits a few inches below the skimmer mouth, since it holds water on top rather than letting it through. A mesh safety cover can sit lower, since it lets rain and snowmelt pass through all winter and the level self-corrects rather than pooling on top of the cover. Check your specific cover manufacturer’s instructions before draining, since overdraining a vinyl liner pool can let it pull away from the wall track.
Whatever the final water level, run your closing numbers through the ClearCove Pools pool chemical calculator so the alkalinity, pH, and calcium doses match your actual gallon count instead of a generic bag-size guess. It’s the same math the calculator uses for opening, just working backward from a full pool.
Next spring, the ClearCove Pools weekly pool care schedule (free download) is the fastest way to get back into a testing rhythm the week the cover comes off, instead of relearning it from scratch.
Frequently asked questions
What temperature should the pool be before closing? Wait until overnight water temperature holds at or below 65°F for several days in a row. Closing warmer water risks algae growth continuing under the cover all winter, a common reason pools open green in spring.
Can I close my pool without draining it? Yes, for most climates. A standard winter close only lowers the water below the skimmer and returns; it doesn’t fully drain the pool. Full drains are reserved for major repairs or resurfacing, not routine winterizing.
Do I really need pool antifreeze if I don’t get hard freezes? If temperatures never drop below freezing in your area, you can often skip antifreeze and just blow out the lines. Anywhere that sees even occasional hard freezes, antifreeze in the lines that can’t fully drain is cheap insurance against a cracked pipe.
How long does closing a pool take? A standard closing, chemistry balancing plus the physical shutdown, usually takes 2 to 4 hours for an experienced owner, spread across the several days needed to let the chemical steps sequence correctly. A professional crew typically finishes the on-site work in under an hour once the pre-close chemistry is already balanced.
Bottom line: balance the water before you shock it, shock before you add algaecide, and never combine the two. Get the chemical sequence right and the physical shutdown, blowout, antifreeze, plugs, cover, is straightforward from there.