How to close an inground pool
Once the water stays below 65 °F, balance it, shock by the label, blow out the lines, drain the equipment, and put on the cover.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (12 sections)
Enter your latest test, and the calculator above plans the balancing doses in the right order. The shock dose comes from your product's label. Example: a 15,000-gallon pool at pH 7.8 and alkalinity 70 ppm needs 4.2 lb of baking soda, then about 13 fl oz of 31.45% muriatic acid.
When to close
Hayward's guidance is to close once the water temperature stays consistently below 65 °F. Closing earlier is the most common reason for a green pool in spring: in warm water, chlorine and winter chemicals are used up long before the cold stops algae. If you have a heater and plan to swim into fall, close when you are done swimming and the water has cooled, not by the calendar.
Plan a two-day window. Day one: balance and shock the water with the pump running. Day two: lower the water, blow out the lines, and take care of the equipment and cover.
Final chemistry and doses
You are setting the water up to sit for months without filtering. Balanced water protects plaster and equipment over winter. A shock clears out anything that would feed algae under the cover.
| Test | Closing target | Why |
|---|---|---|
| pH | 7.4–7.6 (Hayward: 7.2–7.8) | Prevents stains, scale, and etching while the water sits |
| Total alkalinity (TA) | 80–120 ppm | Keeps pH from drifting over the winter |
| Calcium hardness (CH) | 200–400 ppm plaster, 150–250 vinyl or fiberglass (Hayward: 180–220) | Cold water is more aggressive to plaster |
| Stabilizer (CYA) | 30–50 ppm | Protects the chlorine you leave in. You'll see what is left in spring. |
| Free chlorine (FC) | Shock by the product label, then let it fall | Kills algae and breaks down organics before the cover goes on |
- Test and balance alkalinity, pH, and calcium first, with 30 minutes of pump time between products. The calculator at the top does this in the right order.
- Shock in the evening with a product labeled for shocking pools, at the dose on its label scaled to your gallons (a label dose per 10,000 gallons doubles for 20,000).
- Run the pump for 24–48 hours after shocking, as Hayward recommends, and brush and vacuum.
- Winter algaecide, if you use one: Hayward says to let chlorine fall to 1.0–3.0 ppm before adding it. Follow its label for the dose.
Example from our engine: a 20,000-gallon plaster pool at pH 7.7, TA 90 ppm, and CYA 40 ppm needs 12 fl oz of 31.45% muriatic acid to bring pH to 7.5. The shock dose comes from your product's label. For every target in one place, see the pool chemical chart.
Write your readings down. CYA, CH, and TA at closing are next spring's starting point. If CYA reads much lower when you open, that tells you roughly how much water you lost to rain overflow and draining.
Never mix chlorine and acid, or two different chlorine products. Add each separately with the pump running. Add chemicals to water, never water to chemicals, and wear gloves and eye protection. Don't add chemicals right before anyone swims. Don't swim until chlorine is back in your target range. Poison Control: 1-800-222-1222. Always follow the product label. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling.
Lower the water
Water expands when it freezes, so ice can crack the skimmer or the tile. How far to lower depends on your cover. Hayward's numbers:
| Cover | Lower the water to |
|---|---|
| Mesh safety cover | 12–18 in below the skimmer |
| Solid floating cover | 3–6 in below the tile |
Can you close an inground pool without draining it? Yes, and you should: lower it only as far as your cover needs. Use the filter's waste setting or a submersible pump. Do not go lower than you need to. An inground pool relies on the weight of its water to balance groundwater pushing from outside. Pool builders warn that an empty or very low pool can shift or lift. A vinyl liner can also shrink or pull out of its track without water holding it in place.
Blow out and plug lines
Any water left in underground pipes can freeze and crack them. That is the most expensive winter repair. Hayward's closing steps call for blowing out the lines and installing expansion plugs, or adding antifreeze as the manufacturer directs.
- With the pump off, set valves so air can travel from the equipment to the pool.
- Blow air through each line (skimmers, main drain, returns, cleaner line) with a shop vac on blow, a pool line blower, or a compressor set to low pressure. Retail guides favor low pressure and high volume over high pressure.
- When a steady stream of bubbles comes out of a return or skimmer line in the pool, plug that line with a threaded or expansion plug while air is still flowing, so water can't flow back in.
- If you use antifreeze, use only pool or RV antifreeze (propylene glycol), never automotive antifreeze, and only where your equipment maker allows it.
If you are not sure which valve feeds which line, or your area gets hard freezes, this is the one step worth paying a pool service for. A cracked line under the deck costs far more than a service visit.
Equipment
- Drain everything. Hayward says to use the drain plugs to drain the pump, filter, heater, and chlorinator. All water must be drained or blown out so nothing freezes and cracks. Keep the plugs in the pump basket so you find them in spring.
- Clean the filter. Backwash a sand filter, or remove and clean cartridges or DE grids, and store them dry.
- Lubricate the pump lid O-ring and valve O-rings with a pool lubricant.
- Salt cell and chemical feeders: follow the manufacturer's winterizing instructions. Many are removed, cleaned, and stored indoors.
- Power off at the breaker, including the timer and heater, unless your system uses a freeze-protection mode that needs power. Check the manual before switching off a system designed to run in frost.
- Store accessories: ladders, rails, skimmer baskets, cleaners, solar blankets, and hoses (loosely coiled).
Cover
A tight cover keeps debris and sunlight out, which is what keeps the water clear until spring. Hayward prefers mesh safety covers for most pools. Solid covers block more light but collect rain and snowmelt, so they need a cover pump to keep water off them. Check the cover after storms and pump it dry. Standing water on a cover can be a drowning hazard for small children and pets, and leaves that sink through can stain the pool.
In midwinter, if you can, lift a corner and test chlorine once or twice. If it has dropped to zero and the weather is warm, a small top-up of liquid chlorine keeps algae from starting.
What chemicals do you need to close an inground pool?
- A test kit that reads free chlorine, pH, total alkalinity, calcium, and stabilizer.
- A chlorine product labeled for shocking pools, such as liquid chlorine.
- Baking soda (to raise alkalinity) and muriatic or dry acid (to lower pH), as your test calls for.
- Calcium increaser only if a plaster pool tests low.
- Optional: a winter algaecide, added after chlorine falls to its label range.
- For the lines: expansion plugs, and pool or RV antifreeze (propylene glycol) only if your equipment maker allows it.
Closing kits bundle some of these. Check the active ingredients and doses against your own test instead of adding the whole kit by default.
Can you close a pool yourself?
Yes. Most owners can do the chemistry, lower the water, drain the equipment, and put the cover on in a weekend. The step where mistakes cost the most is blowing out and plugging the lines, so hire a pool service for that step if you are unsure. We don't publish closing prices: we could not find current rates we could verify, and they vary by region and by what the visit includes. Ask two or three local services what their price covers (chemicals, line blow-out, cover installation).
Warm climates: keep it running instead
Where the water doesn't freeze, you don't have to winterize. Hayward's mild-climate advice is to cut filtration time roughly in half, keep pH at 7.2–7.8 and free chlorine at 1.0–3.0 ppm, and keep the skimmer clean. We'd add: keep chlorine at or above the minimum for your stabilizer (3 ppm at CYA 40), test weekly, and check your schedule as chlorine loss drops in cool water. Keeping the pool running also means no spring opening.
Above-ground pools close differently (skimmer and return fittings, air pillow, cover cable). See how to close an above-ground pool.
Printable checklist
- ☐ Water has stayed below 65 °F; closing supplies on hand
- ☐ TA, pH, and calcium balanced (30 minutes between products)
- ☐ Shocked at the label dose for your gallons; pump run for 24–48 hours; brushed and vacuumed
- ☐ Winter algaecide added only after chlorine fell to its label range (optional)
- ☐ Closing readings written down (FC, pH, TA, CH, CYA)
- ☐ Water lowered: 12–18 in below skimmer (mesh) or 3–6 in below tile (solid)
- ☐ Lines blown out and plugged; pool antifreeze only if used
- ☐ Pump, filter, heater, and chlorinator drained; plugs kept in pump basket
- ☐ Filter cleaned; O-rings lubricated; salt cell per manual
- ☐ Power off (unless freeze protection needs it); accessories stored
- ☐ Cover on and tight; cover pump ready for a solid cover
In spring, start from the pool opening checklist.
FAQ
Is it better to drain a pool for the winter?
No, not an inground pool. Lower it only as far as your cover requires (12–18 inches below the skimmer for mesh covers, 3–6 inches below the tile for solid covers, per Hayward). A fully drained inground pool can be pushed up by groundwater, and vinyl liners can shrink or pull loose without water holding them in place.
Do I need to winterize my pool?
If temperatures drop below freezing where you live, yes: water in pipes and equipment can freeze and crack them. In climates without freezes, you can keep the pool running on reduced filtration instead of closing it.
What does winterize pool mean?
Preparing the pool to sit unused through cold months: balancing and shocking the water, lowering it, clearing water out of pipes and equipment so nothing freezes, and covering the pool.
Sources
- Hayward, The right time to close your pool (below 65 °F): hayward.com
- Hayward, Ten essential steps to closing your pool (chemistry, water level, equipment, lines, cover): hayward.com
- Hayward, Closing your pool (cold and mild climates): hayward.com
- River Pools (pool builder), How hydrostatic pressure in an inground pool works: riverpoolsandspas.com
- Secondary (retailer guides, blowing lines and pool antifreeze): inyopools.com; intheswim.com
- CDC, Model Aquatic Health Code 2024, Annex (chlorine and CYA): cdc.gov (PDF)