Labor Day has come and gone, the water’s dropping into the 70s overnight, and if you haven’t started thinking about closing your pool, now is the time. Close it too early and you risk algae blooms in warm early-fall water; close it too late and you’re fighting frozen pipes and cracked equipment. For most of the country, the sweet spot is when water temperature holds steady below 65°F (18°C) for about a week, which for much of the U.S. lands somewhere between late September and mid-October.
Here’s a full walkthrough so you can close your pool once this fall and not think about it again until opening day.
1. Deep clean before you cover it
Skim, brush the walls and floor, and vacuum thoroughly. Anything organic you leave behind — leaves, sunscreen film, algae spores — will keep feeding on nutrients under the cover all winter and greet you with a swamp in spring.
2. Balance your water chemistry
This is the step most people rush, and it’s the one that determines how bad your spring opening will be. Test and adjust, in this order:
- pH: 7.2–7.6
- Total alkalinity: 80–120 ppm
- Calcium hardness: 200–400 ppm
- Chlorine (or your sanitizer): shock the pool 24–48 hours before closing
If you’d rather not do the math by hand, plug your pool’s gallons and current readings into our Pool Chemical & Chlorine Dosage Calculator and it will tell you exactly how much of each product to add.
3. Add a winterizing algaecide
A long-lasting, winter-strength algaecide (not your regular summer dose) is cheap insurance against the pool turning green under a dark cover for five months.
4. Lower the water level — but not too far
For pools that will freeze, drop the water level below the skimmer and returns so ice expansion doesn’t crack the fittings. Above-ground pools usually just need a few inches off the top. Don’t drain the pool fully — an empty inground pool can actually pop out of the ground from groundwater pressure.
5. Blow out the lines and add antifreeze
Use a shop vac or dedicated blower to clear water from the skimmer lines, return lines, and filter plumbing, then plug the lines and add pool-specific (non-toxic) antifreeze to the skimmer and any remaining low spots. Skip this step in a freeze-free climate.
6. Drain and store the equipment
Pump, filter, heater, and chlorinator all need to be drained of water and disconnected if there’s any chance of a hard freeze. Store removable parts (baskets, ladders, solar covers) somewhere dry.
7. Cover it properly
A well-fitted safety cover or winter cover keeps out debris, blocks sunlight (which slows algae growth), and is a genuine safety requirement if you have kids or pets around. Make sure it’s pulled taut with no low spots where water and leaves can pool.
8. Keep an eye on it over winter
Check every few weeks: pump standing water off the cover, clear off heavy leaves or snow load, and make sure the water level hasn’t dropped from an unnoticed leak.
9. Write down what you did
Note your closing date, the chemicals and amounts you used, and anything unusual (a stain, a slow leak, a cracked skimmer lid). Future-you, standing in the yard next spring trying to remember, will be grateful.
Closing now vs. waiting
If you’re in a warm-winter climate, you may not need to close at all — just scale back your maintenance routine. If you’re not sure how your fall closing routine compares to how you opened the pool this spring, our guide on mastering your seasonal pool opening walks through the mirror-image process for when it’s time to bring the pool back to life.
Get the chemistry right on the way out, and opening day next year is a five-minute job instead of a weekend project.
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