How to Close a Pool for Winter (Complete Checklist)

If you live somewhere the water actually freezes, closing your pool properly in the fall is what stands between you and a cracked pipe, a heaved skimmer, or a spring opening that costs three times what it should. Winterizing isn't complicated, but it is a specific sequence: balance the water, clean everything, lower the level, clear the lines, and protect what's left. Skip a step and the ice finds it.

When to close

Timing matters more than most people think. Close too early and you're fighting algae growth in water that's still warm enough to support it. Close too late and you risk a surprise freeze catching your equipment full of water. A reasonable rule of thumb: close once water temperature has settled below the mid-60s Fahrenheit and stays there, generally a few weeks before your area's first expected hard freeze. Watching the forecast is more useful than watching the calendar.

Step 1: Balance the water before you close it

This is the step people skip because the pool is about to sit unused anyway, and it's the one that causes the most spring headaches. Water that sits all winter out of balance will spend that whole time etching plaster, staining surfaces, or corroding metal fittings. Test and adjust before you do anything else, using the same targets you'd use during the swimming season.

Pay particular attention to calcium hardness and total alkalinity. Low calcium hardness over the winter can leave plaster surfaces pitted or rough by spring, and alkalinity that's off makes pH swing more than it should while nobody's watching. If a reading is well outside its acceptable range, adjust it now rather than hoping it holds until opening day. Skimmer's water log can hold this closing-day reading so you have an exact baseline to compare against when you reopen.

Step 2: Deep clean before shocking

• Vacuum the pool floor and brush the walls, steps, and any corners where debris settles, working any dirt toward the main drain.
• Skim the surface and empty the skimmer baskets one more time.
• Backwash or clean the filter thoroughly. A dirty filter left to sit all winter is a mildew problem waiting to happen, and you don't want to reopen next season to a filter that needs replacing.
• Remove and clean any pool toys, ladders, or accessories that won't be staying in the water over winter.

Step 3: Shock the water

A winterizing shock treatment gives the water a strong dose of chlorine that keeps working slowly over the following weeks, buying you a head start against algae before everything goes dormant for winter. This is the same breakpoint chlorination math used for a routine shock: roughly 10 times the combined chlorine reading, or a standard 10 ppm dose if combined chlorine is low or unknown. Using standard liquid chlorine at around 12.5% strength, that works out to roughly 1 gallon per 10,000 gallons of pool water for every 10 ppm you're raising free chlorine, or with cal-hypo shock at roughly 65% available chlorine, about 1 pound per 10,000 gallons for the same 10 ppm rise. These are estimates, not exact doses, since actual product concentration varies by brand, so retest free chlorine after dosing and adjust from there. Skimmer's chlorine calculator can work out the right amount for your specific pool volume and product before you buy. Add the shock, run the pump for a few hours to circulate it fully, then move on to the rest of closing while it works.

Step 4: Lower the water level and clear the lines

This is the part that actually prevents freeze damage, and it's not optional in a true freeze climate. Water left sitting in pipes, the pump, the filter, and the skimmer expands when it freezes, and expanding water inside a rigid pipe or fitting will crack it. The fix is to get water out of anything that can't flex.

• Lower the water level below the skimmer opening, typically a few inches, so ice forming at the surface has nowhere to push against the skimmer housing. Follow your specific skimmer and plumbing setup, since exact levels vary by pool design.
• Drain the pump, filter, heater, and any other equipment with standing water inside, using the drain plugs each unit has for this purpose.
• Blow out or drain the plumbing lines (skimmer lines, return lines, and main drain line if accessible) so no water is trapped inside them. This is commonly done with a shop vac set to blow rather than suck.
• Add pool antifreeze (the pool-safe propylene glycol kind, not automotive antifreeze) to lines that can't be fully drained, following the product's instructions for your pipe length.
• Remove, drain, and store any removable equipment like ladders, solar covers, or automatic cleaners somewhere they won't freeze or get sun-damaged over winter.

Step 5: Plug it up and cover it

• Install winterizing plugs (sometimes called Gizzmos or expansion plugs) in the skimmer and return lines to seal them and absorb any ice expansion that does occur.
• Cover any exposed equipment, like the pump and filter, if it's staying outside and isn't otherwise winterized.
• Put on a winter safety cover or mesh cover rated for your pool size, and make sure it's anchored or weighted so wind and snow load can't pull it loose mid-winter.
• Do one final check that the water level, drain plugs, and plumbing lines all look right before you walk away for the season.

What to check during the off-season

A closed pool isn't a pool you never think about again until spring. A quick monthly glance is worth it: check that the cover is still properly seated and hasn't collected standing water or a heavy snow load, and look for any obvious signs of a leak, like a water level that's dropped noticeably more than evaporation would explain. Logging these quick winter checks in Skimmer means you'll have a clean maintenance record heading into your spring opening, and if you ever sell the house, a documented winterizing history is exactly the kind of thing that reassures a buyer the pool has been cared for properly.