How To Close An Above Ground Pool For Winter: A Step-by-Step Technical Guide

Properly closing an above ground pool requires meticulous water balancing, systematic equipment drainage, and the deployment of structural ice expansion barriers. Executing this winterization protocol when water temperatures drop consistently below 65°F (18°C) halts algae spore propagation and protects vinyl liners and plumbing from catastrophic freeze damage. Following these precise steps safeguards your backyard investment, ensuring a seamless, clear, and cost-effective spring reopening.

Critical Pre-Closing Inspections & Equipment Requirements

Closing an above ground pool is not merely about pulling a cover over the top; it is a technical preservation process. The primary objective is to protect the vinyl liner, the metal structural wall, and the filtration system from the expansion of freezing water. Ice expands by approximately 9% in volume, exerting immense pressure outward. Without proper preparation, this expansion can buckle pool walls, split PVC pipes, and crack expensive pump housings.

Before initiating the winterization process, you must gather specialized tools and chemicals. Attempting to winterize without the correct safety gear or chemical agents risks pool structural failure or severe organic staining.

The Winterization Checklist

• Essential Tools & Gear:

  
  
  
  • Submersible cover pump (electric, auto-on preferred, rated for at least 500 GPH)
  • Winter pool cover (matched to pool shape and diameter, with a minimum 4-foot overlap)
  • Heavy-duty vinyl air pillow (typically 4x4 feet or 4x8 feet, 13-gauge or thicker vinyl)
  • Stainless steel cable and winch assembly (usually included with the cover)
  • Pool cover clips (minimum of 2 per top rail) or winter cover wrap (industrial-grade plastic wrap)
  • Threaded winterizing return plugs (usually 1.5-inch MIP threaded plugs)
  • Skimmer faceplate sealing plate (e.g., Aquador system) or a rubber expansion plug
  • Telescopic pole with nylon brush head and manual vacuum assembly

• Mandatory Prerequisite Knowledge & Standards:

  
  
  
  • Water Temperature Threshold: Do not close the pool until the water temperature is consistently below 65°F (18°C). Closing earlier encourages late-season algae blooms under the cover, which consumes winter chemicals rapidly.
  • Liner Sensitivity: Vinyl liners become highly brittle in temperatures below 50°F (10°C). Avoid stretching, scrubbing, or manipulating the liner in cold weather.
  • Local Freeze Depth: Understand your local frost line depth to determine the urgency of thorough pipe drainage.

• Estimated Budget & Duration:

  
  
  
  • Average DIY Budget: $120 to $280 (depending on whether you need a new cover, air pillow, or chemical kit)
  • Time Commitment: 3 to 5 hours of active labor spread over a 24-to-48-hour chemical-balancing window

The Complete Step-by-Step Winterization Protocol

Step 1: Perform Deep Physical Cleaning

Debris left in the pool over the winter decays, causing severe organic staining on the vinyl liner, lowering the pH to acidic levels, and consuming the active winter algaecide.

1. Use a leaf skimmer net to remove all floating organic debris, leaves, and insects from the water surface.
2. Brush the pool walls, stairs, and floor thoroughly using a nylon-bristled brush. This loosens micro-algae film and stubborn dirt clinging to the vinyl pores.
3. Vacuum the pool floor using a manual vacuum set to the "Waste" option on your multi-port valve. If you have a cartridge or simple element filter without a waste option, clean the filter cartridge frequently during the vacuuming process to maintain suction. Vacuuming to waste discharges the debris-laden water directly out of the pool system, preserving your filter media.

Warning: Do not use automated robotic pool cleaners once winterizing chemicals are added, as the highly concentrated chemical shock can degrade the plastic compounds and rubber tracks of the robot.

Step 2: Balance the Water Chemistry for Structural Preservation

Balanced water prevents scale formation, protects metal components from corrosion, and prevents vinyl liner plasticizer leaching, which causes the liner to shrink and become brittle.

1. Test the water using a high-quality liquid drop testing kit (such as a FAS-DPD kit) or take a sample to your local pool professional. Do not rely on expired test strips.
2. Adjust the Total Alkalinity (TA) first. Keep it between 80 and 120 parts per million (ppm). Use sodium bicarbonate to raise TA, or sodium bisulfate (dry acid) to lower it.
3. Adjust the pH to a range of 7.2 to 7.6. This is the optimal range for chlorine efficacy and prevents both acidic corrosion and basic scaling.
4. Adjust the Calcium Hardness to between 200 and 400 ppm. Low calcium levels cause soft water to draw plasticizers directly from the vinyl liner, leading to premature aging and cracking. Add calcium chloride if your levels are below 200 ppm.

Step 3: Administer Winterizing Chemicals

Winter chemicals are formulated to remain active in cold, dark environments over several months.

1. Add a metal sequestrant (chelating agent). This prevents dissolved metals like iron and copper from oxidizing and staining the vinyl liner when chlorine levels shift.
2. Shock the pool with a highly concentrated oxidizing agent. Use non-chlorine shock (potassium monopersulfate) or sodium hypochlorite (liquid chlorine) to raise the Free Chlorine (FC) level to 10–12 ppm. If using calcium hypochlorite granular shock, pre-dissolve it in a bucket of warm water before pouring it along the perimeter to prevent bleaching the vinyl liner.
3. Allow the pump to run for at least 4 to 6 hours to distribute the shock evenly.
4. Add a winter-grade algaecide, such as a copper-free Polyquat 60 (poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylene dichloride] at 60% concentration). Polyquat 60 is highly effective at preventing algae growth without causing metallic staining. Do not add algaecide immediately after shocking; wait at least 12 hours for the chlorine level to drop back down to 3–5 ppm, as extreme chlorine levels can destroy the active ingredients in the algaecide.

Step 4: Draw Down the Water Level Safely

Lowering the water level prevents water from entering the skimmer box and freezing inside, which would split the plastic housing.

1. Determine your winterization method: the "dry skimmer" method or the "Aquador" method.
2. If using the dry skimmer method, use your siphon pump or filter waste line to lower the water level to 4 to 6 inches below the lowest point of the skimmer mouth and the return jet.
3. If using an Aquador skimmer faceplate cover, you do not need to drain the water below the skimmer. Simply snap the plastic lid over the skimmer opening. This retains more water in the pool, providing critical weight to support the pool walls against strong winter winds.

Warning: Never drain an above ground pool completely, and do not lower the water level more than 12 inches below the skimmer. Above ground pools rely on the weight of the water to maintain structural integrity. Without water pressure, the thin metal walls can buckle or collapse inward under high winds or freezing soil pressures.

Step 5: Drain, Disconnect, and Store the Filtration Assembly

Water left inside pool equipment will freeze, expand, and crack the pump volute, filter tank, or chlorinator.

1. Turn off the main breaker to the pool pump and disconnect any timers.
2. Remove the drain plugs from the bottom of the pump basket housing, the filter tank (sand, DE, or cartridge), and the automatic chlorinator if installed.
3. Disconnect all flexible hoses connecting the skimmer to the pump, the pump to the filter, and the filter to the return jet.
4. Store all drain plugs, pressure gauges, and small fittings inside the pump basket so they do not get lost during the winter.
5. If you have a sand filter, set the multi-port valve to the "Winterize" or "Winter" position. This lifts the internal diverter valve off the seat, allowing any trapped water inside the valve head to expand without cracking the plastic.
6. If you have a cartridge or DE filter, remove the internal cartridge element or DE grids, hose them down thoroughly with a filter cleaner, allow them to dry completely, and store them in a dry, rodent-free area.
7. Move the pump motor indoors (to a basement, garage, or dry shed). Humidity and freezing temperatures degrade pump bearings and electrical windings.

Step 6: Plug the Skimmer and Return Lines

Plumbing lines must be sealed to prevent rain or melting snow from re-entering the plumbing.

1. If you lowered the water below the return jet, remove the eyeball fitting from the inside of the pool return. Thread a 1.5-inch MIP winterizing plug (with an O-ring or Teflon tape) into the return line opening until hand-tight, then snug it with a wrench.
2. If using the Aquador faceplate cover, ensure it is snapped securely on the skimmer face. If not, insert a heavy-duty rubber expansion plug (usually size #9 to #11) into the hole at the bottom of the skimmer throat to seal off the drain line completely.

Step 7: Inflate and Position the Air Pillow

The air pillow, often called an "ice compensator," is the most critical mechanical safeguard for an above ground pool. When water on top of the pool freezes, it expands inward. Without a pillow, the solid sheet of ice acts as a wedge, forcing the pool walls outward and tearing the liner. An air pillow absorbs this lateral pressure by compressing under the ice sheet.

1. Inflate the air pillow to only 60% to 80% of its maximum capacity.
2. Tie a heavy nylon rope to the grommets on the corners of the pillow.
3. Center the pillow in the middle of the pool. Tie the ropes loosely to opposite sides of the pool top rails. The ropes must have enough slack to allow the pillow to float naturally on the water surface without being pulled taut, but must be tight enough to prevent the pillow from drifting to one side.

Pro-Tip: Never inflate your pool air pillow to 100% capacity. When temperatures drop, air contracts, but when ice forms, it exerts massive pressure on the pillow. If the pillow is fully inflated to begin with, the sudden pressure will immediately rupture the vinyl seams, rendering it useless.

Step 8: Deploy and Secure the Winter Cover

The winter cover prevents UV rays from destroying your chlorine, blocks leaves, and stops dirt from contaminating the pool water.

1. Drape the winter cover carefully over the pool, positioning it so that it lies flat on the water surface and climbs up the inner walls, draping over the top rails. Ensure the cover lies flush against the air pillow in the center.
2. Thread the vinyl-coated steel cable through the metal grommets around the entire perimeter of the cover.
3. Insert both ends of the cable into the winch (ratchet) assembly. Pull the cable taut by turning the winch handle until the cover is firmly gripped against the underside of the top rail.
4. For areas prone to high winds, install pool cover clips directly over the cover onto the top rails. Use at least two clips per top rail segment to prevent wind from getting under the cover and lifting it.
5. Place a small amount of water (no more than 1 to 2 inches) on top of the cover around the perimeter of the air pillow. This weight stabilizes the cover and prevents it from flapping in high winds.

Winterization Chemical Standards & Operational Benchmarks

The table below outlines the precise chemical levels and physical parameters required to protect your above ground pool during the winterizing process.

Resolving Structural & Environmental Winter Failures

Scenario 1: The Air Pillow Shifts to One Side or Deflates

• Root Cause: If the holding ropes are tied too tightly, the wind will pull the pillow to one side, or the tension will rip the plastic grommet holes, causing a slow air leak.
• Actionable Fix: Use heavy-duty duct tape or vinyl patch kits to seal any visible punctures in the pillow. Re-inflate it to 70% capacity. When anchoring, tie the ropes diagonally across the pool, leaving several inches of slack so the pillow floats freely but is kept centered. Do not pull the ropes taut.

Scenario 2: Ice Storms Pull the Cover Into the Pool

• Root Cause: Heavy accumulation of water, melting snow, and ice on the cover creates a downward force that exceeds the holding strength of the cable and winch assembly.
• Actionable Fix: Never attempt to physically shovel heavy snow or break solid ice off the cover, as shovels and sharp ice shards will puncture the pool cover and the vinyl liner below. Instead, place an electric submersible cover pump directly onto the cover during warmer, above-freezing afternoons to drain accumulated meltwater. Keep the cover cable tightened by ratcheting the winch monthly.

Scenario 3: Water Levels Drop Rapidly Under the Cover

• Root Cause: A slow leak has developed in the pool liner. When water levels drop below the frost line, the weight of the ice on the cover can pull the pool walls inward, causing structural buckling.
• Actionable Fix: Slide a small underwater repair kit patch onto the leak if it can be found from under the cover. If the leak is inaccessible, you must run a hose under the cover to add water back to the pool to maintain the 4-to-6-inch level below the skimmer. This prevents wall collapse. Do not let the pool sit dry or semi-dry during freezing weather.

Scenario 4: Algae Bloom Observed Under the Cover During Winter Thaws

• Root Cause: The pool was closed too early when the water was warm, or the winter cover is not UV-opaque, allowing sunlight to penetrate and reactivate dormant algae.
• Actionable Fix: Peel back one corner of the cover near the pool wall. Pour in one gallon of liquid chlorine (sodium hypochlorite) directly into the water. Use a pool brush on a telescopic pole to gently agitate the water under the cover to distribute the sanitizer. Re-secure the cover immediately.

Frequently Asked Questions

Can I leave water in my above ground pool during winter?

Yes, you must leave water in your above ground pool during the winter. The weight of the water provides the necessary internal pressure to keep the thin metal walls of the pool from collapsing inward from wind and freezing ground forces. You should only lower the water level 4 to 6 inches below the skimmer to protect your plumbing.

Should I inflate my pool air pillow all the way?

No, never inflate a pool air pillow to 100% capacity. It should only be inflated to about 60% to 80% of its total capacity. This leaves enough room for the pillow to compress when the pool water freezes into ice, absorbing the lateral pressure instead of popping the pillow or buckling the pool walls.

How do I prevent my above ground pool cover from blowing off in high winds?

To prevent your cover from blowing off, tighten the perimeter cable with the winch assembly until it is snug beneath the top rail. Then, install pool cover clips directly over the cover onto the pool's top rails. For extreme wind areas, wrap the perimeter of the pool several times with commercial-grade pool cover wrap (similar to heavy plastic cling wrap) to block wind from getting under the cover edge.

When is the best time to close an above ground pool?

The optimal time to close an above ground pool is in late autumn, once the pool water temperature drops consistently below 65°F (18°C). Closing the pool when the water is warmer than this encourages algae growth and bacteria to consume the winterizing chemicals, leading to a green, swampy pool when you open it in the spring.

Protect Your Investment with Professional Care

Properly winterizing your pool now saves hundreds of dollars in liner repairs and replacement chemicals when spring arrives. Keep your pool safe throughout the winter by checking the cover tension and pumping off excess rainwater regularly.