How To Close My Above Ground Pool For The Winter: The Definitive Step-by-Step Guide

Safely closing an above ground pool for the winter requires a precise sequence of chemical balancing, water level adjustment, hydraulic line drainage, and physical structural reinforcement. By maintaining a pH of 7.2 to 7.6, utilizing an ice compensator pillow to absorb lateral freezing forces, and winterizing filtration equipment, you protect your pool liner and structural walls from catastrophic cold-weather damage. Executing these steps correctly ensures a seamless, crystal-clear opening when spring arrives.

Pre-Closing Engineering and Equipment Checklist

Before beginning the physical winterization process, you must coordinate your closing schedule with local weather patterns. Closing your pool too early—specifically when ambient water temperatures are still consistently above 65°F (18°C)—creates an ideal environment for algae spores to consume winterizing sanitizers and bloom under the cover. Wait to initiate this process until the water temperature drops and remains below this threshold.

Proper preparation prevents structural wall collapse under wind loads and avoids ruptured plumbing lines due to ice expansion. Gather all necessary equipment, specialized tools, and winterizing chemicals in advance to ensure an uninterrupted workflow.

Essential Materials, Tools, and Prerequisites

• Chemical Winterization Kit: Must contain a non-chlorine oxidizing shock, a highly concentrated chelating metal sequestrant, and a high-molecular-weight polymer algaecide (preferably Polyquat 60 to avoid copper staining).
• Expansion Plugs and Seals: Heavy-duty rubber expansion plugs (typically size #9 to #11 for standard 1.5-inch return lines) or threaded winter plugs with O-rings.
• Skimmer Closure Systems: A watertight skimmer faceplate seal (such as an Aquador system) or a heavy-duty winterizing skimmer plug.
• Ice Compensator (Air Pillow): One or more heavy-gauge vinyl air pillows (typically 4x4 feet or 4x15 feet depending on pool shape and size).
• Pool Cover Assembly: A solid, UV-resistant winter cover matching your pool dimensions, complete with a vinyl-coated steel cable and a heavy-duty aluminum ratchet winch.
• Support & Protection Tools: A submersible pool cover pump, a soft-bristle pool brush, a leaf skimmer net, and heavy-duty winter cover clips or wall-bags.
• Mandatory Technical Knowledge: Your pool’s exact gallon capacity, local freeze depth metrics, and the manufacturer-specified weight limit of your pool's top ledges.
• Operational Benchmarks:
  
  
  • Estimated Budget: $120 to $300 (depending on chemical choices and cover quality).
  • Required Time: 3 to 5 hours of active, continuous labor.

The Complete Above Ground Pool Winterization Process

Follow these steps in exact chronological order. Skipping or rearranging these steps can result in chemical imbalances that ruin the vinyl liner, or trapped water that splits expensive filtration equipment.

Step 1: Execute a Comprehensive Deep Clean

Any organic debris left in the pool over the winter will decay, staining the vinyl liner and consuming the sanitizer reserves meant to keep the water clear until spring.

1. Use a leaf skimmer net to clear all floating organic matter, leaves, and insects from the water surface.
2. Brush the pool walls, steps, and floor thoroughly using a nylon-bristle wall brush to break up any microscopic biofilm or early-stage algae colonies.
3. Vacuum the pool floor. If there is a high volume of silt or debris, set your multi-port filter valve to the "Waste" position to pump the debris directly out of the system, bypass the filter medium, and preserve the filtration system's capacity.
4. Empty the skimmer basket and pump strainer basket of all accumulated organic material.

Step 2: Establish Hydraulic and Chemical Equilibrium

Proper chemical balance prevents scaling, metal staining, and liner degradation over the winter months. Cold water alters chemical solubility, making balanced water even more critical during sub-freezing thaws.

1. Test your water using a reliable liquid reagent test kit or bring a sample to a professional pool station.
2. Adjust the Total Alkalinity (TA) first to sit between 80 and 120 parts per million (ppm). This stabilizes your pH and prevents rapid fluctuations.
3. Adjust the pH to a range of 7.2 to 7.6. If pH is too low, the water becomes acidic and will corrode metal components and compromise the elasticity of the vinyl liner; if too high, it leads to scale formation and reduces sanitizer efficacy.
4. Verify that your Calcium Hardness is between 200 and 400 ppm. Soft water will attempt to draw calcium directly out of the vinyl liner, making it brittle and prone to tearing.
5. Pour a heavy-duty chelating metal sequestrant directly into the pool. This prevents dissolved iron, copper, and manganese from oxidizing and permanently staining your liner while the pool sits stagnant.

Step 3: Implement Shock Treatment and Algae Prevention

Adding sanitizers and algaecides in the correct order is vital. High chlorine levels can break down and neutralize the active ingredients in your winter algaecide.

1. Broadcast a non-chlorine oxidizing shock (potassium monopersulfate) across the pool surface at the manufacturer’s recommended dosage. This eliminates organic contaminants without raising the chlorine concentration to liner-damaging levels.
2. If using traditional chlorine shock, raise the free chlorine level to 10-12 ppm and allow the pool filter to run for at least 12 to 24 hours. Let the free chlorine level fall back down to its normal range of 1 to 3 ppm before proceeding to the next step.
3. Add a concentrated, copper-free Polyquat 60 algaecide. Polyquat algaecides are positively charged polymers that attach to negatively charged algae cells, rupturing their outer walls. Avoid cheap copper-based algaecides, which can cause purple or green staining on vinyl liners over long periods.
4. Run the filtration system for at least one full cycle (usually 6 to 8 hours) to distribute the winter chemicals evenly throughout the entire water column.

Step 4: Lower the Water Level or Install a Skimmer Shield

To protect your skimmer housing from cracking under the pressure of freezing water, you must choose one of two distinct winterizing methodologies.

Warning: Do not drain an above ground pool completely, and avoid lowering the water level more than 12 inches below the skimmer. Above ground pools rely on the weight of the water inside to resist external wind loads and maintain structural roundness. Excessive draining can cause the pool walls to collapse inward during high winter winds.

• Method A: The Traditional Drawdown Method. Lower the water level using your filter's "Waste" setting or a submersible pump until the water is 3 to 6 inches below the bottom of the skimmer mouth and the return jet line.
• Method B: The Faceplate Cover Method (Highly Recommended). Install a watertight skimmer faceplate cover (such as an Aquador). This snap-on plastic lid seals the skimmer opening completely, allowing you to keep the water level at normal operating height. This preserves the structural integrity of your pool walls and saves water.

Step 5: Drain and Winterize the Hydraulics and Equipment

Water expands by approximately 9% when it freezes, generating up to 114,000 pounds per square inch (psi) of pressure. Any water left trapped inside your pump, filter, or plumbing lines will freeze, crack the heavy plastic housings, and destroy the equipment.

1. Disconnect the flexible hoses linking the skimmer to the pump, and the filter to the return inlet. Drain these hoses completely, roll them up, and store them indoors.
2. Remove the drain plug at the bottom of your pump strainer housing. Allow all water to drain, then run the pump for a brief 2 to 3 seconds to expel any residual water from the impeller housing. Store the pump inside a climate-controlled area.
3. Winterize your filter based on its medium type:
   
   
   • Sand Filters: Remove the drain cap at the bottom of the tank. Set the multi-port valve to the "Winterize" or "Closed" position. Store the multi-port valve indoors if possible.
   • Cartridge Filters: Open the air relief valve, unscrew the drain plug, and open the filter tank. Remove the cartridge elements, spray them thoroughly with a cartridge cleaner, rinse, dry, and store them indoors.
   • Diatomaceous Earth (DE) Filters: Drain the tank completely. Remove the DE grids, flush them clean of all old DE powder and organic oils, and store them safely.
4. Install a threaded or expanding rubber expansion plug into the return jet line from the inside of the pool. If you opted for Method A (lowering the water level), ensure the return line is dry before plugging it.

Step 6: Deploy and Center the Ice Compensator (Air Pillow)

The primary function of an air pillow is not to hold up the pool cover, but to act as a sacrificial pressure absorber (ice equalizer) for the pool walls.

1. Inflate the heavy-gauge vinyl air pillow to only 60% to 80% of its maximum capacity.

2. Pro-Tip: Do not over-inflate the air pillow. A fully inflated, rigid pillow cannot compress when ice builds up. It will pop under pressure, rendering it useless. The pillow must remain somewhat soft and pliable to absorb lateral ice expansion forces.

3. Tie heavy-duty nylon ropes to the grommets on the corners of the pillow.
4. Position the pillow directly in the center of the pool. Secure the ropes to the outer structural upright posts of your pool, ensuring the pillow stays centered. When ice forms, it will freeze from the outer walls inward, pushing the soft pillow inward rather than bowing your pool walls outward.

Step 7: Secure the Winter Cover and Winch System

The pool cover must shield the water from sunlight and prevent airborne debris from contaminating the clean water.

1. Drape your winter pool cover over the pool and the centered air pillow. The cover should rest loosely on the surface of the water and up over the air pillow; do not pull it tight like a drum head.
2. Thread the vinyl-coated steel cable through the metal grommets around the perimeter of the cover.
3. Insert the ends of the cable into the aluminum ratchet winch. Pull the cable tight against the outer wall of the pool, underneath the top ledge. Ratchet the winch until the cover is completely secure against the pool wall.
4. Install heavy-duty winter cover clips along the top rail to prevent wind from catching the lip of the cover. For areas prone to high winds, wrap the perimeter of the pool cover with several layers of heavy plastic winter wrap.
5. Place a submersible pool cover pump on top of the cover to drain off accumulated rainwater and melted snow throughout the winter.

Winterizing Chemical Targets and Physical Specs

Use the following reference guide to ensure all chemical and physical parameters are maintained within their engineered ranges prior to sealing the pool cover.

Winter Pool Pitfalls: Failure Scenarios and Immediate Fixes

Even when following strict guidelines, environmental factors can cause issues mid-winter. Use these diagnostic remedies to resolve common problems before they cause permanent damage.

Scenario 1: The Air Pillow Pops or Deflates Mid-Winter

• Root Cause: The air pillow was over-inflated prior to closing, or a slow leak developed along the heat-welded seams due to pressure from heavy snow loads.
• Actionable Fix: Do not attempt to remove the entire winter cover. Use a long extension pole with a blunt hook to pull the deflated pillow toward the edge of the pool. Slide a new, partially inflated pillow under the cover using a pool pole, and secure its ropes to the outer vertical uprights.

Scenario 2: Water Accumulates on Top of the Cover, Dragging it Down

• Root Cause: Failure to run a cover pump, or a rip in the cover allowing pool water to seep through, equalizing the water level and creating a vacuum.
• Actionable Fix: Place a weighted submersible cover pump in the center of the cover. Pump the water off the cover and away from the pool structure. If the water being pumped out contains pool chemicals or matches the color of your pool water, you likely have a tear in the cover. Patch the tear with a vinyl repair kit or replace the cover immediately.

Scenario 3: Algae Growth Visible During a Mid-Winter Thaw

• Root Cause: The pool was closed when the water temperature was too high, or the winter cover is not UV-blocking, allowing sunlight to fuel photosynthesis.
• Actionable Fix: Peel back one corner of the winter cover near the return line. Pour 1 to 2 gallons of liquid chlorine shock directly into the water. Use a pool brush or a manual pool pole to agitate and distribute the chemical. Re-secure the cover immediately.

Scenario 4: The Pool Wall Buckles Under the Skimmer Housing

• Root Cause: Water leaked into the skimmer housing and froze, or the water level inside the pool was lowered too far, making the pool walls vulnerable to strong winter winds.
• Actionable Fix: If wind buckling occurs, do not attempt to pop the metal wall back into place while it is freezing cold. Secure the pool cover cable tighter to stabilize the structure. When spring arrives and the ice thaws, carefully use a rubber mallet and a block of wood from the inside of the pool wall to gently tap the metal wall back into its original position before refilling.

Frequently Asked Questions

Can I close my above ground pool without lowering the water level?

Yes, you can close your pool without lowering the water level if you install a watertight skimmer faceplate seal (such as an Aquador). This seal isolates the skimmer throat from the pool water, allowing you to drain the skimmer housing and plumbing lines while keeping the pool completely full. Keeping the water at normal operating height provides maximum structural stability against heavy winter winds.

When is the best time of year to close my above ground pool?

The ideal time to close your pool is in the autumn when the ambient pool water temperature drops and remains consistently below 65°F (18°C). Closing the pool before the water cools down encourages rapid algae growth under the winter cover, resulting in a swampy, green pool opening in the spring.

Should I use an air pillow if I live in an area that doesn't freeze?

If you live in a warm climate that does not experience freezing temperatures, an air pillow is not structurally necessary. However, it can still be helpful because it holds the center of the cover up, forcing rainwater and debris toward the edges of the pool where it is much easier to clear away with a pool cover pump or leaf skimmer.

How do I prevent strong winter winds from getting under my pool cover?

To stop wind from lifting your cover, use specialized plastic winter cover clips that snap directly onto your pool's top rails. You can also wrap the outer perimeter of the pool cover and the pool wall with multiple layers of heavy-duty industrial stretch wrap. Never weigh down your cover with cinder blocks or bricks resting on the top rails, as this can bend and damage the metal frame.

Do I need to empty my sand filter completely before winter?

Yes, you must remove the drain cap at the bottom of your sand filter tank and leave it off for the entire winter. Any water trapped inside the sand bed will expand as it freezes, which can easily crack the heavy fiberglass or plastic filter tank, requiring a complete replacement of the filter system.

Secure Your Pool for the Coming Winter

Protect your backyard investment and avoid costly spring repairs by securing your pool before the first hard frost. Shop for high-quality winter covers, non-chlorine shocks, and durable ice-equalizing air pillows to ensure your pool survives the cold season without damage.