How to Close an In-Ground Pool for Winter

Here in the Arizona desert, we don’t close our pool the way most of the country does. But the first fall after my sister bought a house in Colorado, she called me in a panic with a pool, a pile of equipment she didn’t understand and a hard freeze in the forecast. I flew up for a long weekend, and we closed it together with her owner’s manuals spread across the patio table.

We made one big mistake that year: we closed too early, while the water was still warm, and opened to a green swamp in spring. Since then I’ve helped close her pool every fall, and the routine below is what we’ve settled on. It works for most in-ground pools with a mesh or solid safety cover.

When to close

Close once the water stays below roughly 65°F, but before your first hard freeze. Warm water feeds algae, so closing in early September often means a messy opening. Waiting too long risks freezing water in the plumbing, which can split pipes and damage equipment. Watch the extended forecast and plan for a dry day.

If you live where freezes are rare and brief, you may not need to close fully. Many warm-climate owners keep the pump running on a shorter schedule all winter and use a freeze-protection setting instead. Check what’s normal for your area.

What you’ll need

• Test kit and the chemicals to balance pH and alkalinity
• Chlorine shock and a winterizing algaecide
• Brush, skimmer net and vacuum
• Submersible pump or the filter’s waste setting to lower the water
• Shop vac or blower, winterizing plugs for returns and lines, and a skimmer plug or ice-expansion device
• Pool antifreeze made for pool plumbing (never automotive antifreeze), if your area needs it
• Your winter cover, water bags or anchors

The fix, in order

1. Balance the water a few days ahead. Test and adjust pH and alkalinity first, then calcium hardness if your surface needs it. Balanced water protects plaster and equipment from scale and etching while the pool sits.
2. Clean it thoroughly. Skim, brush the walls and floor, and vacuum. Empty the skimmer and pump baskets. Anything left in the pool becomes food for algae over the winter.
3. Shock, then add winterizing algaecide. Shock the pool following the label and let the pump circulate it. Wait until chlorine falls back toward the normal range before adding a winterizing algaecide, since very high chlorine can reduce some algaecides’ effectiveness. Follow both products’ directions and never mix them together.
4. Clean the filter. Backwash a sand or DE filter, or remove and clean cartridges. A clean filter makes spring opening much easier.
5. Lower the water level. How far depends on your cover and climate. With a mesh safety cover, many owners lower the water below the skimmer mouth, often to a few inches below the returns. Some solid covers need the water higher to support them. Your cover manufacturer’s instructions are the final word.
6. Blow out and plug the lines. Use a shop vac or blower to push water out of the skimmer and return lines until you see bubbles at the far end, then seal each one with a winterizing plug. In cold regions, many owners add pool antifreeze to the lines as backup. Put a skimmer plug or an ice-expansion device in the skimmer.
7. Drain the equipment. Turn off power at the breaker. Remove the drain plugs from the pump, filter, heater and any chlorinator, and let them empty completely. Store the plugs in the pump basket so you can find them in spring. Store small removable parts indoors if the manufacturer recommends it.
8. Cover the pool. Remove ladders and rails. Install the cover snugly according to its instructions, with springs tensioned evenly on a safety cover or water bags placed edge to edge on a solid cover. Keep a cover pump handy to remove rainwater and snowmelt from solid covers.

Common closing mistakes

• Closing while the water is still warm. Algae keeps growing under the cover.
• Skipping the line blowout. Water left in pipes can freeze, expand and split fittings or underground plumbing.
• Using car antifreeze. It’s toxic and not meant for pool systems. Only use antifreeze labeled for pools.
• Losing the drain plugs. Store them together where you’ll see them at opening.
• Ignoring the cover all winter. Standing water and heavy debris can stretch or damage a cover. Check it after storms.

When to call a pool pro

• You’re not sure how to blow out your specific plumbing, or you have a complex system with a spa, waterfalls or multiple valves.
• You have a gas heater and aren’t confident draining and shutting it down properly.
• You notice leaks, a damaged pool surface or broken equipment while closing.
• A hard freeze is coming and you can’t close in time. Many pool services offer closing visits.