Pool closing is the lowest-glamour day of the pool calendar and the highest-leverage one. A correct closing means a clean, swim-ready pool 7 days into spring opening. A sloppy closing means cracked pipes, stained walls, green water, and a 4-week recovery before anyone gets in. The work itself is straightforward if you follow the sequence. Skipping any of the steps below is what causes the most expensive winter damage to inground pools.
This checklist assumes a typical residential inground or above-ground pool of 30000 to 80000 liters in a climate that sees freezing temperatures. Mild-winter readers can skip the line blow-out section but should still complete the chemistry and cover steps.
Step 1: deep clean and pre-closing chemistry
Start 5 to 7 days before the actual closing date. The pool should be visibly clean (no floating debris, no algae bloom, no cloudiness) when you start winterizing because anything left in the water will multiply over 5 months under the cover.
Brush walls and floor thoroughly. Vacuum on the waste setting if your filter has a multiport valve, otherwise vacuum slowly and clean the cartridge afterward. Empty pump baskets and skimmer baskets. Backwash sand or DE filters. Inspect the liner or plaster for stains and address with a stain treatment now (the chemistry is far easier to apply with the system running than after winterization).
Five days out, bring chemistry into a tight range: free chlorine 2 to 3 ppm, pH 7.4 to 7.6, total alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm. Cyanuric acid (stabilizer) should be at 30 to 50 ppm. Pools that go into winter with low stabilizer burn through chlorine on the first warm spring days and open green.
Step 2: closing shock and algaecide
48 hours before the cover goes on, shock the pool with calcium hypochlorite at 30 grams per 10000 liters and run the pump for 24 hours. The shock dose drops to a normal 2 to 3 ppm free chlorine residual by closing day, which is the ideal level for the cover-on period.
Once free chlorine has dropped to 3 ppm or below, add a polyquat 60 percent winter algaecide at the dose specified on the bottle (typically 30 ml per 10000 liters for a closing dose). Polyquat is the only algaecide that performs well through a 5-month cold-water dormancy. Cheap copper-based algaecides stain the liner and gas off over winter. Add a stain and scale preventer (sequestrant) at the same time to lock up dissolved metals that would otherwise plate out on the walls as the pool cools.
Run the pump for at least 8 hours after dosing.
Step 3: drop water level and remove accessories
Drop the water level using the multiport valve on waste setting, or a submersible pump. The target level depends on pool type:
- Vinyl liner pool with skimmer: 15 cm below the skimmer mouth
- Concrete pool with skimmer: 15 cm below the skimmer mouth
- Fiberglass pool with wall skimmer: 15 cm below the return jets, NOT below the skimmer (manufacturer-specific, check your pool’s documentation)
- Above-ground pool with skimmer: 5 to 10 cm below the skimmer
Drop too far and a vinyl liner can pull away from the track at the top edge. Stay above the lower limit and you keep enough water to weigh the pool down through winter (important for fiberglass and concrete shells in high water table soils).
Remove ladders, handrails, diving boards, robotic cleaners, solar covers, and any other accessories. Store them indoors. Rinse them with fresh water before storage to prevent corrosion at fasteners.
Step 4: blow out the plumbing lines
This is the single most important step for any freeze-prone climate. Trapped water in PVC or flex lines expands when it freezes and splits the pipe. Repairs run from 200 dollars (one accessible joint) to 5000 dollars (cut concrete decking to reach a buried main line).
Connect a wet-dry shop vac (on blow mode) or a small air compressor to the pump’s drain plug port. A 6 horsepower shop vac is the sweet spot for a residential pool. Larger compressors push 100+ psi which can blow off equipment seals.
Work outward from the pump. Blow each return line until you see steady bubbles at the wall return, then plug the return jet with an expandable rubber winterizing plug. Move to the skimmer line and blow until bubbles appear in the skimmer, then plug the skimmer line at the bottom of the skimmer with a Gizzmo (a sacrificial plastic plug that absorbs freeze expansion). Blow main drains and pour 4 liters of pool antifreeze (non-toxic, propylene glycol based) into each plugged line as a backup. Never use automotive antifreeze (ethylene glycol) in pool plumbing.
Drain the pump, filter, heater, chlorinator, and any in-line accessories. Remove pump drain plugs, filter drain plugs, and heater drain plugs and store them in the pump basket where you will find them in spring. Loosen quick-connect unions on the pump suction and discharge sides. Remove the pressure gauge from the filter (water in the gauge freezes and cracks the housing).
Step 5: install the cover
A safety cover (mesh or solid) anchored to deck-mounted brass anchors is the right choice for any inground pool. Cost runs 1200 to 3000 dollars for a custom-fit cover that lasts 12 to 15 years. Pull the cover taut and ratchet each anchor strap. The cover should sit 15 to 30 cm above the water surface in a slight dome, not touching the water.
Above-ground pools use a winter cover secured with a cable and winch, plus optional air pillows under the cover to absorb ice expansion. Add 2 or 3 inflated air pillows in the center for an above-ground pool in a freezing climate.
Install a cover pump on the cover surface for solid-cover installations. Without one, 200 to 400 liters of rainwater and snow melt can collapse a solid cover by midwinter.
Step 6: equipment shutdown and indoor storage
Disconnect electrical at the pump breaker. Tag the breaker so no one energizes a dry pump in spring. Bring small accessories indoors: chlorinator cap and check valve, pressure gauge, pool light bulb (if removable), cleaner hoses, and the pump strainer basket.
Schedule a midwinter cover check 60 days after closing. Walk the perimeter, check anchor tension, pump off any standing water on a solid cover, and brush off accumulated leaves on a mesh cover. This 10-minute check is the difference between a clean spring opening and a green-water surprise in March.
Frequently asked questions
When should I close my pool for winter?+
Close when water temperature drops below 15 degrees Celsius (60 Fahrenheit) for a full week and stays there. In most of the United States that lands between mid-September and early November. Closing too early (above 18 degrees) traps warm water under the cover where algae will bloom over winter. Waiting until water hits 5 degrees risks a freeze event before the lines are blown out, which can crack plumbing and cost 1500 to 4000 dollars to repair.
Do I need to drain my pool to winterize it?+
No, full draining is the wrong approach in almost every climate. Drop the water level 15 to 30 cm below the skimmer (or below the return jets if you have a fiberglass pool with a wall skimmer) so the lines can be blown clear and freeze damage stays contained. A full drain risks liner shrinkage in vinyl pools and ground-water uplift in fiberglass and concrete pools.
How much does professional pool closing cost in 2026?+
A standard professional closing for an inground pool costs 300 to 600 dollars in 2026 including line blow-out, chemistry, plug installation, and cover. Above-ground pool closings cost 200 to 400 dollars. Winterizing chemical kits sell separately at 60 to 150 dollars. DIY closing costs only the chemicals plus a rented air compressor for line blow-out (about 50 dollars per day) if you do not own one.
What chemicals do I need for closing?+
A full closing kit covers shock (calcium hypochlorite or non-chlorine shock), winter algaecide (polyquat 60 percent), pH adjusters, and a stain and scale preventer. Total cost runs 60 to 150 dollars for a 50000 liter pool. Skip chlorine tablets in the skimmer over winter because they will not dissolve in cold water and they corrode metal parts as they slowly degrade.
Can I leave my pool uncovered for winter?+
In climates where water never freezes (USDA zone 9b and warmer) you can run a pool year-round without a cover, on reduced pump hours and reduced chemistry. In any climate with regular sub-zero overnight temperatures, an uncovered pool is a freeze damage waiting to happen and a debris trap. Even a basic mesh safety cover for 400 dollars pays for itself in saved chemistry within one season.
Priya Sharma
Priya Sharma writes for The Tested Hub.