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When Should You Close Your Pool in Connecticut?

Most Connecticut pools should close when water drops below about 65 degrees. Here is how timing differs from the shoreline to the Litchfield Hills.

When Should You Close Your Pool in Connecticut?

Most Connecticut pools get closed sometime between mid September and mid October. The better answer, though, comes from a thermometer rather than a calendar: close when the water stays below about 65 degrees Fahrenheit.

That number matters because algae slows way down in cool water. Close a pool at 78 degrees over Labor Day weekend and you are sealing warm, sunny water under a cover for six months, which is how people end up with a green swamp in April.

If your pool is still open this first week of October, you are not late. In much of the state, this is right in the sweet spot.

The 65 Degree Rule of Thumb

Pool pros around New England use the same general guide. Once the water temperature holds in the low to mid 60s for several days, algae and bacteria grow slowly enough that winter chemicals can keep the water clear until spring.

A cheap floating thermometer is all you need to track it. Check it in the late afternoon for a week or so, when the water is at its warmest, and look for a steady downward trend rather than one cold morning.

In most Connecticut towns, that trend lands somewhere in late September or early October. Heated pools are the exception, since owners can run the heater into October and then shut it off a week or two before closing so the water can cool.

Why Closing Too Early Backfires

The pull to close early is understandable. Kids are back in school, the weather turns, and nobody is swimming after the first chilly weekend in September.

The problem is that sunlight and warm water keep feeding algae for weeks after the swimming stops. A cover blocks some light, but if the water is still in the 70s, your winter shock and algaecide will get used up long before the season is over.

Early closers often open in spring to murky or green water that takes days of shocking, brushing, and filtering to clear. That can mean $100 to $300 in extra chemicals, or a green-to-clean service call that runs higher. Leaving the pump running a few extra weeks costs much less.

Shoreline Towns Versus the Litchfield Hills

Connecticut is small, but the closing window still shifts depending on where you live. Proximity to Long Island Sound and elevation both change how fast water cools.

A pool in Madison, CT and one in Norfolk, CT might be ready to close three or four weeks apart. Your neighbors' timing is a better guide than a statewide date.

Along the shoreline

From Greenwich up through Guilford and Old Saybrook, the Sound keeps nights milder well into fall. Shoreline pools often stay above 65 degrees until late September or early October, and many owners close around mid October.

The tradeoff is that shoreline towns see heavy leaf fall from mature oaks and maples around the same time. Waiting too long means skimming leaves daily until the cover goes on.

Inland and in the hills

In the Litchfield Hills and the northwest corner, around Litchfield, CT, Torrington, CT, and Norfolk, cold nights arrive sooner. Water often drops into the low 60s by mid to late September, and first frost is common by early October.

The Hartford area and the central valley land in between. Many pools there close in late September or the first two weeks of October.

How Late Is Too Late?

The real deadline is freezing. Water left in pipes, skimmers, the pump, the filter, and the heater can freeze, expand, and crack components that cost hundreds or thousands of dollars to replace.

A light frost or a single night just below freezing will not usually hurt a running system, since moving water is slow to freeze. Several nights in the mid 20s with water sitting still in the lines is where damage starts.

For most of Connecticut, the safe window closes somewhere around late October or early November. If you push it that far, keep the pump running on cold nights and have the closing booked, since pool companies fill their October calendars quickly.

What a Proper Closing Involves

A good closing protects both the water and the equipment. Whether you do it yourself or hire a pro, the basic sequence looks like this:

1. Test and balance the water, getting pH, alkalinity, and calcium hardness in range a few days before closing.
2. Brush, vacuum, and skim so no leaves or debris sit on the floor all winter.
3. Add winter shock and algaecide according to the product directions.
4. Lower the water level below the skimmer and return lines, or to the level your cover manufacturer recommends.
5. Blow out every plumbing line with a shop vac or blower, then plug the lines at the pool side.
6. Add pool antifreeze to the lines if your setup calls for it.
7. Drain the pump, filter, heater, and chlorinator, and store removable parts indoors.
8. Remove ladders, rails, and accessories, then install the winter or safety cover.

Blowing out the lines is the step most likely to go wrong for a first-time DIYer. If you are not sure every line is clear, it is worth paying someone at least the first time.

Leaves, Trees, and Picking a Cover

Much of Connecticut sits under hardwood trees, and fall color is lovely until it lands in your pool. A yard with oaks, maples, or pines overhanging the water will feel every week you delay closing.

A leaf net placed over the pool before the main drop, or on top of a solid cover, saves a lot of work. You pull it off full of leaves, shake it out, and put it back.

Solid tarp covers are the cheaper option but collect rain and snow, so you will need a cover pump and water bags. Mesh or solid safety covers anchor into the deck, hold weight, and are much safer around kids and pets. A new custom safety cover typically costs roughly $1,500 to $4,000 installed, depending on size and shape.

DIY or Hire a Pro?

Doing it yourself mostly costs time and supplies. A winterizing chemical kit runs about $40 to $100, pool antifreeze roughly $10 to $20 a gallon, and plugs, water bags, and a cover pump can add $100 to $250 if you do not already have them.

A professional closing in Connecticut generally costs about $250 to $500 for an inground pool and roughly $175 to $350 for an above-ground pool. Pools with heaters, spas, waterfalls, or automatic covers usually land at the higher end or above it.

Many local companies bundle closing and spring opening together at a small discount. If you want to compare providers, browse our list of pool service companies in your area and book early, since fall slots fill up fast.

Keeping an Eye On It Over Winter

Closing the pool is not quite the end of the job. A Connecticut winter throws rain, heavy snow, ice, and the odd January thaw at your cover, and a quick look every couple of weeks prevents most problems.

On a solid cover, keep the cover pump running or check it after every storm so water does not pool in the middle and stretch the fabric. Snow on a safety cover is fine in normal amounts, but ice dams along the edges and water bags that have split should be fixed when the weather allows.

Check the pool water level if you can see it at the edges. A sudden drop may point to a leak, while water rising close to the tile line after a wet winter can put pressure on skimmers and the cover.

Above-Ground Pools Follow Slightly Different Rules

Above-ground pools in Connecticut usually close on the same 65 degree cue, but the process is simpler. Most owners lower the water just below the skimmer and return, disconnect and store the hoses, pump, and filter indoors, and use an air pillow under the cover to handle ice expansion.

The freeze risk is lower because there is little buried plumbing. The bigger worry is the liner and cover, since wind can get under a loose cover in a nor'easter and tear it or dump debris into the water.

Thinking Ahead to Spring Opening

The work you do now shows up in April or May. A pool closed at the right temperature, with balanced water and clean lines, often opens with clear or slightly hazy water that clears in a day or two.

Most Connecticut pools open in May, once daytime temperatures reach the 70s and the water starts warming. Shoreline owners sometimes open a little earlier, while hill towns often wait until late May.

A professional opening usually costs about $250 to $500, similar to closing. For more seasonal home care tips, visit our home services blog.

Pool Closing Questions

Can I close my pool in early September in Connecticut?

You can, but it raises the odds of algae by spring. If the water is still above 70 degrees, waiting two to four more weeks and running the filter usually pays off.

What if the leaves have already started falling?

Put a leaf net over the pool and keep skimming until the water cools. Leaves left on the floor under a cover can stain the finish and feed algae all winter.

Do I need antifreeze in my pool lines?

Many Connecticut pool owners add it as insurance after blowing out the lines. A gallon or two per line, at roughly $10 to $20 a gallon, costs much less than a cracked pipe.

How much does it cost to close a pool in Connecticut?

Most professional closings run about $250 to $500 for inground pools. DIY closings usually cost $100 to $300 in chemicals and supplies.