Pool closing isn't optional in freezing climates. Water left in lines and equipment expands when it freezes and cracks pipes, fittings, filters, and pumps. A bad winterization can cost more in spring repairs than the entire pool season. The work is methodical: balance water first, then drain to the right level, blow lines clear, protect everything that can freeze, shock and treat to last through winter, and cover. Hire a pool service if you've never done it; the difference between a $0 closing and a $1,500 spring repair is doing the steps right.

When to close

  • When daytime temps consistently drop below 65°F.
  • Before first hard freeze in your area.
  • Not too early: closing while water is still warm can cause algae to bloom under the cover.
  • Not too late: closing after the first freeze risks pipe damage between forecast and the actual close.
  • In most northern US, late September to mid-October is the standard window.

Quick sequence

  1. Test and balance water chemistry (a week before close).
  2. Clean the pool: skim, brush, vacuum.
  3. Backwash or clean the filter.
  4. Lower water level below the skimmer inlet (4 to 6 inches for solid cover, 12 inches for mesh).
  5. Blow out lines with a shop vac or hire a pool service.
  6. Add pool antifreeze (non-toxic, NOT automotive) to lines per the manual.
  7. Install winter plugs in returns; seal the skimmer with a skimmer plug or Gizzmo.
  8. Drain and store pump, filter, chlorinator, heater per the manufacturer.
  9. Shock the pool with high-dose chlorine.
  10. Add winter algaecide and stain/scale treatment.
  11. Install the cover and weight or secure it.
  12. Remove and store ladders, handrails, accessories.

Balance the water first

Test and adjust chemistry a week before close to give chemicals time to settle. Closing with unbalanced water means winter chemistry drifts even further and spring opening is a struggle.

  • pH: 7.4 to 7.6.
  • Total alkalinity: 80 to 120 ppm.
  • Calcium hardness: 200 to 400 ppm (plaster), 150 to 250 (vinyl).
  • Free chlorine: 1 to 3 ppm at balance, then shock to higher levels at close.
  • Cyanuric acid: 30 to 50 ppm.

See how often to test pool water.

Clean before closing

  • Skim leaves, bugs, and debris.
  • Brush walls and floor.
  • Vacuum the pool fully. Anything left becomes part of the winter chemistry.
  • Empty skimmer baskets and pump basket.
  • Backwash sand filter or clean cartridge filter elements.

Lower the water level

  • Solid cover: water 4 to 6 inches below the skimmer or tile line. Lower water level keeps it out of the skimmer mouth where it could freeze.
  • Mesh cover: water 12 inches below skimmer. Rain and snow melt enter through the mesh and refill toward the skimmer; you want margin.
  • Use the pump (set to waste/drain) or a submersible pump to lower water.
  • Don't drain a vinyl liner pool fully. The water weight holds the liner in place; draining can let it shift.
  • Don't drain a fiberglass pool below 2 feet. Empty fiberglass shells can "pop" out of the ground from groundwater pressure.

Blow out the lines

Water left in plumbing lines freezes and cracks pipes. Two approaches:

  • Shop vac (DIY): connect a wet/dry vac in blow mode to the pump or skimmer line and push air through until water stops coming out of returns. Some pool plumbing layouts are easy to blow; others (with main drains, multiple returns, water features) get complicated.
  • Air compressor / pool service: commercial air compressors at the right pressure are what pool service techs use. Faster and more thorough. Often worth the $150 to $400 service fee for peace of mind.

This is the step where DIY mistakes cost the most. If you've never blown lines, watch a video for your specific pool layout or hire the close once and watch what the tech does.

Antifreeze and plugs

  • Use only non-toxic pool antifreeze (usually pink). Don't use automotive antifreeze in pool plumbing under any circumstances. Toxic to people and pets if it leaches into the pool come spring.
  • Add antifreeze to each line per the manufacturer's instructions, typically about 1 gallon per 10 feet of pipe.
  • Install winter plugs in return lines after blowing them out.
  • Seal the skimmer with a skimmer plug or insert a Gizzmo (a flexible plastic tube that absorbs ice expansion).
  • Cover the skimmer with a winter cover plate to keep out debris.

Equipment

  • Pump: drain by removing drain plugs, store indoors if possible.
  • Filter: drain sand or DE filter via drain plug; remove and store cartridge elements indoors.
  • Chlorinator: drain and clean. Salt chlorinator cells often come off and store indoors.
  • Heater: drain per manufacturer. Some heaters need a winterization kit or specific drain sequence.
  • Light fixtures: check that they're submerged enough not to freeze and crack.

Shock and winter treatment

  • Shock the pool with cal-hypo or liquid chlorine at the higher dose listed for closing (often 2 to 3x normal shock).
  • Add winter algaecide per the product label.
  • Add stain and scale preventer if your water chemistry pushes that way.
  • Run the pump for an hour after adding chemicals if equipment isn't already winterized. If equipment is winterized, the water won't circulate; the cover and cold water mostly keep chemistry stable.

Install the cover

  • Safety cover (anchored mesh): install per manufacturer; the anchor system goes into the deck.
  • Solid cover: place over pool, secure with water bags or weights around the perimeter. Install a cover pump on the cover surface to remove rainwater.
  • Cover pump: essential for solid covers. Water that accumulates on a solid cover weighs hundreds of pounds and can tear the cover or sink it.
  • Inspect cover for tears or weak spots before installing.
  • Don't walk on solid pool covers. They're not strong enough to support a person.

Accessories and decking

  • Remove ladders and handrails. Store indoors.
  • Remove skimmer baskets and other removable parts.
  • Clean and store pool toys, floats, cleaners.
  • Cover or store furniture if you want to preserve it from winter weather.
  • Trim back tree branches that overhang the pool area.

Through winter

  • Monthly: pump water off solid covers; check cover for damage.
  • After heavy snow or storms: inspect the cover and pump off accumulated water.
  • Don't lift the cover to "peek" except for serious reasons; air exposure restarts algae growth.
  • If a major freeze is forecast and you have any doubt about line winterization, run a slow trickle of water through any visible plumbing (some service companies do this).

When to hire a pro

  • First time closing this pool.
  • Complex plumbing (main drains, multiple returns, water features, automatic covers, integrated spa).
  • Heater requires winterization kit you don't have.
  • You'll be away during the close window.
  • The pool froze and there's damage to assess.
  • Pool service rates for a close are typically $200 to $600, much less than the cost of a single cracked pipe.

Good maintenance rhythm

  • Yearly in fall when temps drop below 65°F: full pool close per the checklist.
  • Monthly through winter: pump cover water; inspect cover.
  • After every major storm: check cover and equipment exposed to weather.
  • Yearly: inspect winter cover for tears and replace if frayed.
  • Spring (mid-60s temps consistent): open per the pool opening checklist.
  • Ongoing: photograph the close each year so spring opening reverses the right steps.
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