Best Pool Winterizing Kit
The best pool winterizing kit for most in-ground pools is a sized all-in-one closing kit like the In The Swim Pool Winterizing Kit, because it bundles the three chemicals that actually protect a dormant pool (a winter algaecide, an oxidizer, and a stain and scale preventer) in one box matched to your gallons. Understand this before you spend a dollar: a winterizing kit is chemicals only. It is not a cover, it does not include skimmer plugs, and it will not blow out your lines. Buying the kit and skipping the cover, the plugs, and the water-level drop is how people open to a green, cracked mess in spring. A kit earns its place by getting the chemistry right so the water stays clear under the cover for five or six months with no circulation. Once you accept that, the choice comes down to sizing it to your real water volume, whether you close a fussy metal-stained pool, and whether your pool is above ground. Here are the picks, and what actually matters when you buy.
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In The Swim Pool Winterizing Kit
Who it is for: In-ground pool owners who want one box, sized to their gallons, with everything the water needs to sit clear until spring.
- +Bundles the three chemicals that matter for a dormant pool: a winter algaecide, a chlorine-free oxidizer, and a stain and scale preventer, so you are not guessing what to buy separately.
- +Sold in sizes matched to your water volume (roughly up to 7,500, 15,000, 24,000, and 35,000 gallons), which is the whole point of a kit: the doses are pre-portioned for your pool.
- +Includes clear step-by-step closing instructions, so a first-timer adds things in the right order instead of dumping everything in at once.
Watch out: It is chemicals, not a full closing. You still need a winter cover, skimmer and return plugs, and a lowered water level in freeze climates. Match the size to your real gallons with the pool volume calculator, and follow the full sequence in how to winterize a pool. Doheny's sells a near-identical closing kit if you find it cheaper.
Robelle Winter Pool Closing Kit
Who it is for: Owners who want a cheaper kit they can order from Amazon in the same gallon sizes and have it show up in two days.
- +The same three-part formula (algaecide, oxidizer, stain and scale) at a lower price than the pro brands, sold in the standard gallon-range sizes.
- +Widely stocked online and in big-box stores, so it is the easy grab when you decide to close on a cold weekend.
- +Fine for a well-balanced pool that gets a tight cover; the value tier does the job when the water goes in clean.
Watch out: The algaecide in budget kits is often a weaker, lower-percentage quat, so a pool prone to algae or one closed for six-plus months benefits from adding a stronger polyquat (see the upgrade pick below). Qualco and Rx Clear sell comparable value kits if Robelle is out of your size.
Winter Air Pillow plus a small closing kit
Who it is for: Above-ground pool owners, where the winter threat is ice pushing out on the walls, not just algae.
- +A winter air pillow floats under the cover and takes the ice load, so expanding ice pushes in on the pillow instead of out against your pool walls; on an above-ground pool that is the failure that actually wrecks the pool.
- +It also props the cover up into a slight dome so rain, snow, and leaves run to the edge instead of pooling in a sagging pocket in the middle.
- +Pair it with a small-gallon closing kit (Robelle or In The Swim) and you have the two things above-ground pools need: the chemistry and the ice protection.
Watch out: Size the pillow to your pool (4x4 for small round pools, 4x8 or larger for big ones) and double up on very large pools. It is an add-on, not a substitute for the closing chemicals. Do not overinflate it; leave it soft so it can compress. A cover pump on top keeps water off the cover, covered in best pool cover pumps.
Polyquat 60 winter algaecide
Who it is for: Anyone closing for a long winter, or a pool that opens green every spring no matter what.
- +A 60 percent polyquat (such as In The Swim Algaecide 60 Plus or Kem-Tek Algaecide 60) is non-metallic and low-foaming, and it lasts far longer through a dormant season than the cheap 10 percent quat in a bargain kit.
- +Because it is non-metallic it cannot stain the surfaces the way copper algaecides can, which matters when it sits in still water for months.
- +It is the single highest-value add to any kit for a pool with a history of spring algae; you add it last, after the shock chlorine has dropped.
Watch out: Do not add polyquat at the same time as a high shock level; chlorine degrades polyquat, so shock first, let free chlorine fall back toward normal, then add the algaecide with the pump running before you cover. This is the same non-metallic chemistry covered in best pool algaecide.
What actually matters when buying
What is actually in a winterizing kit?. A closing kit is three chemicals, sometimes four. A winter algaecide (ideally a polyquat) so nothing grows in still, uncirculated water; a shock or oxidizer to burn off the last of the season's organics before the pump goes off; and a stain and scale preventer (a sequestrant) that holds dissolved metals and hardness in solution so temperature swings do not drop them onto the walls as stains. Some kits add a clarifier or an oil-absorbing pillow. That is the whole job of a kit: get those chemistries into balanced water so it sits clear with no filtration for months.
Size the kit to your real gallons, not the box label. This is the one number that decides which kit to buy. Kits are sold by gallon range, and a kit sized for 15,000 gallons under-doses a 25,000-gallon pool, which is exactly how a pool opens green. Buy the size that covers your actual water volume, and round up if you are between sizes. Do not trust the pool's advertised size; work out your real gallons with the pool volume calculator first, then pick the kit.
Balance the water before you add the kit. A kit does not replace balancing, and adding it to off-balance water wastes it. Get pH, total alkalinity, and calcium hardness into range before you close, because a stain and scale preventer cannot fully compensate for water that is corrosive or scaling, and low pH makes any metal in the water more likely to stain. Check your targets against ideal pool chemistry levels and fix each reading with the matching tool before dosing the kit. Do not guess a closing shock amount from the box; size it with the pool chlorine calculator.
A kit is not a cover, plugs, or an air pillow. The most common mistake is thinking the kit closes the pool. It does not. You still need a winter cover, plugs for the skimmer and returns, a lowered water level, and blown-out or antifreeze-protected lines in any climate that freezes. On an above-ground pool add an air pillow to take the ice load. The chemicals keep the water clean; the cover, plugs, and water-level work protect the plumbing and the shell. Pick the cover in best pool covers and follow the physical steps in how to winterize a pool.
Close at the right time, and store leftovers right. Wait until the water holds consistently below 60 degrees Fahrenheit, because algae go dormant below that and closing a warm pool just breeds a bloom under the cover; the full reasoning is in when to close a pool for winter. Buy the kit close to when you will use it so it is fresh, and store any leftover algaecide or sequestrant cool, dry, and sealed for spring, following how to store pool chemicals safely. Never save an opened bag of shock next to acid.
How we picked
This is a research-based guide. We compared what closing kits actually contain (winter algaecide chemistry, oxidizer type, and stain and scale sequestrant), how they are sized by gallon range, staining and foaming risk, and a broad set of owner reviews across the established closing-kit brands. We do not bench-test products, and we take no payment for placement. Chemistry claims reflect well-documented facts: polyquat outlasts cheap quat through a dormant season, chlorine degrades polyquat so the two are added apart, and a sequestrant holds metals in solution. Always dose to your tested, balanced water and follow the product label and the size for your real gallons.
Keep your water right, too
Gear handles the cleaning; chemistry is the other half. Useful next: how to winterize a pool, when to close a pool for winter, how to open a pool, best pool covers, pool volume calculator.
Frequently asked questions
What do you put in a pool to winterize it?
Three chemicals do the chemical side of closing: a winter algaecide (a 60 percent polyquat is the durable choice), a shock or oxidizer to clear the last organics before the pump goes off, and a stain and scale preventer that keeps dissolved metals and hardness from dropping onto the walls over the cold months. A closing kit bundles all three, sized to your gallons. That is only half the job, though; you also lower the water, plug the lines, and cover the pool. Balance pH, alkalinity, and calcium against ideal pool chemistry levels first, and follow the physical steps in how to winterize a pool.
What order do you add pool closing chemicals?
Balance first, then add the stain and scale preventer (the sequestrant) and let it circulate so it binds the metals. Add the shock or oxidizer next and run the pump to spread it. Add the algaecide last, after the free chlorine from the shock has dropped back toward a normal level, because a high chlorine level degrades polyquat and wastes it. Run the pump one final time to mix the algaecide, then lower the water, plug the lines, and cover. The short version: sequestrant and shock first with the pump running, algaecide last.
Do you put algaecide or shock in first when closing a pool?
Shock first, algaecide last. Chlorine degrades polyquat algaecide, so adding them together at a high chlorine level burns up the algaecide before it can protect anything through winter. Shock the pool, let the free chlorine fall back toward its normal range over a day or so, then add the algaecide with the pump running just before you close. If your kit's instructions say otherwise, follow the label for that specific product, but keeping a strong shock dose and the polyquat apart is the safe default.
How much does it cost to winterize a pool?
Doing it yourself, the chemicals are the cheap part: a sized closing kit runs roughly 30 to 80 dollars depending on your gallons, plus a cover and plugs you reuse each year. A professional closing service, where a crew blows out the lines, plugs everything, and covers the pool, typically runs about 150 to 400 dollars or more depending on pool size, plumbing, and region. Many owners pay for the blow-out the first year to learn it, then handle the chemistry and cover themselves after that. The kit itself is the smallest line item.
Can you close a pool without chemicals?
In a freeze climate you can never skip the physical steps: you still must lower the water below the skimmer, blow out or antifreeze the lines, and plug them, or you risk cracked plumbing. Skipping the chemicals is a gamble. If the water is perfectly balanced, you close early, and the cover is tight, some owners get away with just a sequestrant. Most who skip the algaecide and oxidizer open to green or stained water in spring and spend more clearing it than a kit would have cost. When you reopen, you do not buy a separate kit; you balance, shock, and clear, as in how to open a pool.