How to Close a Pool for Winter (Hard-Freeze Close vs. Florida "Winter Mode")

“Closing the pool” means two entirely different jobs depending on where you live, and the internet mashes them together. In Pennsylvania it means draining the plumbing so it doesn’t split and sealing the pool under a cover for five months. In Florida it means almost nothing — you keep the pool open, dose it less, and have a plan for the two or three nights a year it drops below freezing.

Do the northern procedure in Tampa and you’ve paid to shut down a pool you could have swum in. Skip the northern procedure in freeze country and you’ll be replacing plumbing in April. So: pick your track first.

Which close do you need?

• Hard-freeze close — if your pool water reliably drops below 60°F for weeks and your air goes below freezing for sustained stretches. Full drain-and-cover procedure.
• Warm-climate “winter mode” — Florida, the Gulf Coast, coastal Southern California, south Texas. The pool stays open. You reduce, rebalance, and prepare for freeze nights.

Above-ground pools have their own procedure in both cases, and it gets its own full section below — not a footnote.

Florida “winter mode” — the close that isn’t a close

Trouble Free Pool’s own cool-weather guidance opens by acknowledging it plainly: some pool owners live in climates where a pool can be left open throughout the year. That’s most of Florida. Here’s what actually changes.

Your chlorine demand drops — a lot

The sun angle in December is much lower, so it burns off far less chlorine. The amount you need to maintain the water slows dramatically. Keep testing, but expect to add a fraction of what you added in July. Don’t “keep the schedule” out of habit and overshoot — test first, then dose.

Your salt cell is going to quit, and that’s normal

This is the single most common winter panic call in Florida, and it isn’t a broken cell. Salt chlorine generators stop producing in cold water on purpose, to protect the cell:

• Pentair IntelliChlor: turns off at 52°F, ±3°F and will not produce chlorine.
• Hayward Aqua Rite: automatically stops generating below 50°F.

Both are documented in the manuals. Hayward notes this is usually not a problem because bacteria and algae stop growing at that temperature. When your cell goes quiet, switch to liquid chlorine for the duration — it’s the cheap, clean way to hold FC through a cold snap. (More on cell behavior and lifespan in how long does a salt cell last.)

Cut pump run time, don’t cut it out

With cold water and low chlorine demand, you can minimize pump run time and run only enough to keep the chemicals mixed. That’s a real saving — and it’s the same logic as why 24/7 pumping is a myth in summer, just further along the curve.

Keep pH up so the surface doesn’t etch

Cold water shifts your saturation index down. The guidance is to raise pH to keep CSI above -0.6 so a plaster surface doesn’t etch. This is the one number worth watching harder in winter than in summer — see water balance and LSI/CSI.

Leave the heater alone below 70°F

Some manufacturers of gas heaters warn that cycling the heater on and off when the water is under 70°F can damage it. If you’re not actually heating for a swim, don’t tease it.

The freeze night plan — this is the part that matters

Florida gets a handful of nights a year in the 20s and low 30s. That’s when pools get hurt, and it’s entirely preventable:

1. Run the pump. Moving water is difficult to freeze, so circulate as much as possible. Pentair’s pump manuals say the same thing in their own words: in mild climate areas, when temporary freezing conditions may occur, run your filtering equipment all night to prevent freezing.
2. Set the valves so every pipe gets flow. Figure out a valve setting that makes at least a bit of water pass through each pipe and each piece of equipment. A dead leg is where the split happens.
3. Don’t trust the pump’s built-in “freeze” feature to protect the pool. Variable-speed pumps have a cold-weather mode — Pentair’s Thermal Mode defaults to a 40°F set point at 20% speed — but Pentair explicitly says not to rely on it, because it reads the internal drive temperature, not the air. Hayward is even blunter: its Low Temp Operation “is NOT intended to protect the pump, system plumbing, or pool from freezing.” These features protect the pump’s electronics, not your plumbing. If you’re unsure whether your freeze protection is working, turn it off and set the system to run 24/7 manually until the freeze passes.
4. Have a power-outage plan. Freeze nights and outages travel together. Know how to drain your equipment quickly — find the drain plugs on your pump pot, filter, and heater before you need them in the dark. Wrap exposed plumbing, tarp the pad, keep a couple of cut-up pool noodles or a half-full plastic jug to drop in the skimmer, and shut off and purge the autofill. If you have a heater, it’s best to let water run through it, but do not activate heat mode.

That’s Florida winter. No cover, no blower, no antifreeze — just less chlorine, less pump, higher pH, and a plan for three cold nights.

Hard-freeze close — in-ground

This is the real procedure. There are many ways to winterize a pool, varying both by how far north or south you are and by personal preference — but the order below is the one that consistently produces a clear opening in spring.

1. Wait for the water to drop below 60°F

Not the air — the water, and solidly below. Below 60°F algae is fairly unlikely to grow, and when it does, it grows very slowly. Closing early is the number-one cause of a green opening, because you’ve sealed a pool that can still grow algae into a dark box for five months. Also don’t cut it so fine that the equipment has no time to drain and dry before the first hard freeze.

While you wait, let the water level drift down toward the bottom of the skimmer instead of topping it off. It saves you draining time later.

2. Balance the water

Bring pH to 7.4-7.6 and make sure TA and CH are in their recommended ranges. This is the chemistry that will sit in your pool for five months — if it’s aggressive now, it’s aggressive all winter against a surface you can’t see. The 5 numbers covers what “in range” means.

3. SLAM two or three days before, then let FC drift down

Two or three days ahead, raise chlorine to SLAM level for your CYA and hold it until FC holds overnight (which it usually does on the first night). Then let FC fall to 20% of your CYA — typically another day and a half. You’re closing with the water proven algae-free and chlorine at the low end of normal, not at shock level.

4. PolyQuat, then clean

Add the startup (maximum) dose of PolyQuat per the package. Then clean up leaves and dirt in the water. Don’t chase every leaf that falls in while you’re finishing — that’s what the cover is for. (Note what’s not on this list: a “winterizing kit” of mystery chemicals. See is the pool store a scam.)

Pull ladders, handrails, toys, and anything removable and store it. Ladders can fight you — release every clamp and lock, then wiggle with a helper.

5. Lower the water level — but read your cover manual first

The cover dictates this step, not the pool. An automatic cover needs full water support. Safety covers specify a maximum water depth from the cover. Consult the cover manual before you drain anything. And note the trap: auto-covers are designed to rest on the pool water — you will damage the auto-cover if you drain the pool and then close it.

If the cover permits, drain by pool type:

Two additional cautions from the closing wiki: with mesh safety covers, keeping the water within 18 inches of the top of the pool matters a lot for reducing stress on the cover (Meyco’s guidance). And with a plaster pool, don’t leave the waterline sitting exactly at a step or ledge — leave an inch of water above any step or ledge, so the freeze line isn’t parked on an edge.

The easiest way to drain below the skimmer is your own pump with a vacuum hose rigged as if you were manually vacuuming, so it stays primed. If it keeps losing prime, switch to the cover pump.

6. Remove fittings, then blow the lines

Pull the skimmer baskets and the return eyeballs.

Blowing the lines is where people over-do it and break things. The physics is reassuring, not scary: you only need about 3.5 psi to clear a pipe 8 feet below water level, and typical 2” pool plumbing has a bursting pressure around 890 psi. So the goal is volume, not pressure. Both manufacturers are explicit — Pentair and Hayward both warn not to purge the system with compressed air, because components can explode, and to use only a low pressure (below 5 PSI), high volume blower. A dedicated pool blower is the right tool; a shop vac on blow can work on simple plumbing.

Push air through until nothing but a very fine mist comes out the other end (the return jet), give it a little extra, then install the winterizing plugs.

Two things worth knowing:

• You do not, and cannot, clear the main drain of water. The goal is to push water down that pipe to at or near the frost line, then leave it.
• The skimmer’s real protection is displacement. Once the skimmer line is blown out, the point is to get water out of the skimmer body so that if ice forms, it has room to expand upward. Ice doesn’t expand more than about 9%, and it will go up. That’s what the antifreeze-plus-noodle-foam trick in the skimmer is actually doing.

7. Pull the drain plugs and pull the cell

Remove the drain plugs on the pump, filter, and heater. Both Pentair and Hayward tell you the same thing about the pump — remove both drain plugs from the strainer pot, drain it, and store the plugs in the strainer basket so they’re there in April. Protect exposed drain-plug holes with non-hardening joint compound to prevent rust.

Salt systems: remove the SWG cell assembly along with sensors and any acid tank. Hayward’s Aqua Rite manual adds a useful distinction — drain all water from pump, filter, and lines because the cell and flow switch freeze just like plumbing, but the electronic control head is built to take winter weather and should not be removed.

Filters have their own steps, and they’re the ones most often skipped:

• Sand, multiport valve (Pentair): backwash, shut the pump off, open the air bleeder, and set the valve to WINTERIZE — leave it there until the system restarts. Remove the filter’s drain plug and store it. Pentair’s reason for the winterize position is that it takes pressure off the valve diverter’s rubber seal all season.
• Sand (Hayward S200): there’s no named winter position — drain the tank by unscrewing the drain cap, leave the cap off, and set the valve handle between two positions so water drains out of the valve. Leave it in that inactive spot.
• Cartridge: pull the drain plug and leave it off — Hayward’s SwimClear manual says leaving it unattached avoids cracking the filter body. Remove the PSI gauge and take it indoors. Clean the cartridges and store them indoors, not in the filter, and reinstall at opening.

8. Antifreeze — propylene glycol only

Add pool/RV antifreeze at about one gallon per ten to fifteen feet of pipe. A curved funnel makes getting it into the return line far easier.

Never automotive. Pool and marine antifreeze is propylene glycol; engine coolant is usually ethylene glycol and does not belong anywhere near a pool. Hayward says it in the manual: use only propylene glycol, because it’s non-toxic and won’t damage plastic system components, while other antifreezes are highly toxic and may damage them.

Then seal the pipes with expandable rubber plugs — skimmer line, return line, and the unions the SWG attached to. The skimmer gets most of a gallon of antifreeze on top of the plug plus some torn-up pool noodle foam.

9. Lights: check the manual, not the forum

Winterizing pool lights varies enormously by light type, closing method, location, and how deep your ice shelf gets. Your first resource is the light’s owner’s manual — some manufacturers give very specific instructions and some say nothing at all. Depending on those factors the light may safely stay installed below the waterline, or it may need to come out (and the conduit sealed). Some owners wrap a removed light and set it on the deck; others suspend it deeper in the water, below the potential ice shelf. There is no single standard method — ask people who close pools in your specific area.

10. Cover it, then keep an eye on it

Center the cover, press the edges so it lies flat on the water and runs up the wall, and lay the rest flat on the deck. Ring it with water bags filled one half to two thirds full (that’s the room they need to freeze without splitting), tucking excess cover underneath so nothing flaps.

Then, through the season:

• Leave a cover pump on as long as overnight temps stay above freezing, in both fall and spring.
• Once the leaves are down and dry, clear them off with a blower or long-handled rake.
• Check periodically — water bags leak, and a big storm can blow one onto the cover.
• Once an ice shelf forms, leave it alone. It’s generally advised not to break or disturb it, and that’s doubly true on a vinyl liner, which sharp ice tears easily.

Above-ground closing — the full procedure

Above-ground pools are not “in-ground, but smaller.” The walls are the thing you’re protecting, the plumbing is external and comes off, and one whole category — soft-side pools — gets taken down entirely.

Rigid-wall above-ground (steel/resin wall, permanent install)

Timing. Begin well before any danger of freeze so the equipment has time to fully drain and dry — but don’t close too early. Same 60°F rule: wait for the water to get down to 60°F or lower.

Chemistry. Same as in-ground — balance, SLAM it clean ahead of time, let FC settle, add PolyQuat.

Water level. Drain to about 6 inches below the lowest return or skimmer opening, and remove the hoses and fittings. Hayward’s own skimmer instructions for the Dyna-Skim line say the same six inches and add the part that explains why: be sure the skimmer is kept free of water accumulation, because warranty does not cover damage caused by ice forming in the skimmer.

Plugs are your call. This is where a lot of confident internet advice is simply wrong. Trouble Free Pool’s above-ground procedure says it directly: skimmer and return plugs or “gizmos” may be installed or they may be left open — this is a personal choice for each pool owner. What isn’t optional is getting the water out of the skimmer.

Equipment. Drain the pump and filter well and remove the pump, hoses, and fittings. On a multiport, remove the spider gasket — leaving it compressed all winter is what flattens it. Smaller fittings, hardware, and filter drain plugs can live inside the pump pot basket; lube the pot with silicone lube. Store the pump, smaller filter systems, and the spider gasket indoors. For a large sand filter that stays outside, secure a heavy trash bag or tarp over it against debris, snow, ice, and water.

Cover, and what the pillow actually does. The cover should touch the water and be supported by air pillows or by water. The pillow’s documented job is preventing the cover from sagging into the gap between the top of the pool and the lowered water line — that’s it. It is widely repeated that the pillow absorbs ice expansion and saves your walls; we could not find that claim in a single manufacturer document, so treat it as folklore, not engineering. Also plan for the pillow to fail: air pillows often don’t stay inflated for the season and are found deflated at opening. In heavy-snow country, an above-ground cover can pull the sides inward if it isn’t properly supported — that’s the real structural risk, and it’s a support problem, not an ice-cushion problem.

Leaf net. A leaf net over the winter cover is a good move while leaves are still dropping — but remove the net and the debris it caught before hard freeze. A frozen-in leaf net is a spring problem.

Ice shelf. Same rule as in-ground, and it matters more here: once it forms, don’t break it. Vinyl tears.

The take-down option. You can also drain and clean the pool and store the liner and frame in a dry place. One warning from people who’ve done it: liners stored outdoors or in a shed have been found with small holes where rodents chewed through the vinyl. Store it somewhere sealed.

Soft-side above-ground (Intex, Bestway and similar)

Completely different rules, and the manufacturer is unambiguous. Intex’s Easy Set manual: you must drain, disassemble and properly store the pool when the temperature drops below 41°F (5°C) — ice damage can result in sudden liner failure or pool collapse. That is a hard instruction, not a suggestion, and it does not transfer to steel-wall pools.

If your winter never gets to 41°F and you choose to leave it up, Intex’s own leave-up procedure is: clean the water thoroughly, remove the skimmer, plug the inlet and outlet fittings from inside the pool, remove the ladder, remove the hoses connecting pump and filter, add the appropriate chemicals, clean and drain the pump/filter housing/hoses, discard the old filter cartridge (keep a spare for next season), and bring the pump and filter parts indoors to a dry place between 32°F and 104°F.

Bestway’s sand filters get winterized on their own terms too: drain the tank, pour the sand out completely, dry all components, and store the unit in a dry place out of reach of children.

The mistakes that cost the most

• Closing while the water is still warm. Cheapest mistake to avoid, most expensive to fix — you’re locking algae in the dark with a food supply.
• Blasting the lines with a compressor. Both major manufacturers warn against it. Volume, not pressure. Under 5 PSI.
• Automotive antifreeze. Ethylene glycol. Never.
• Draining a pool with an automatic cover and then closing the cover. The cover is designed to float on the water; without it, you’re damaging the cover.
• Leaving the cartridge in the filter, or the pressure gauge outside. Both are cheap parts that freeze-crack for no reason.
• Trusting a variable-speed pump’s freeze mode to save your plumbing. It reads its own drive temperature and both manufacturers explicitly say it isn’t for that.
• Counting on the air pillow to protect the walls from ice. It’s cover support. Plan around it deflating.

Bottom line: figure out which winter you actually have. If it freezes hard, close in order — wait for 60°F, balance, SLAM and drift, drop the water to what your pool and cover want, clear the lines with volume not pressure, pull every drain plug, propylene glycol only, and cover it. If you’re in Florida, don’t close at all — dose less, run less, keep pH up, switch to liquid chlorine when the salt cell goes quiet, and run the pump straight through the two or three freeze nights a year. Either way, when it’s time to reverse it, how to open a pool in spring picks up exactly where this leaves off.