How To Close An Above Ground Pool: The Complete Winterization Guide

Successfully closing an above ground pool requires a systematic approach to balancing water chemistry, protecting the filtration system from expansion damage, and securing the structure against the weight of snow and ice. By maintaining a pH between 7.2 and 7.6 and utilizing air pillows to displace ice pressure, you can prevent structural failure and ensure a crystal-clear reopening in the spring.

Pre-Winterization Inventory and Strategic Planning

The process of closing an above ground pool, often referred to as winterizing, is not merely about putting a lid on the water. It is a critical maintenance phase designed to protect your investment from the destructive forces of freezing temperatures and stagnant water. Failure to winterize correctly can lead to cracked pump housings, torn vinyl liners, and compromised pool walls due to the immense lateral pressure of ice.

Before beginning the physical labor, ensure you have the following specialized materials and tools on hand. Waiting until the temperature drops below freezing is the most common mistake made by pool owners; ideally, the closing process should commence once the water temperature consistently remains below 65 degrees Fahrenheit (18 degrees Celsius) to inhibit algae growth.

Essential Equipment and Materials Checklist:

• Winter Chemical Kit: Including pool shock (calcium hypochlorite or non-chlorine), winter algaecide, and a metal sequestering agent.
• Water Testing Supplies: High-accuracy liquid drop test kit or digital tester.
• Cleaning Tools: Telescopic pole, skimmer net, pool brush, and vacuum head.
• Winter Cover & Hardware: A reinforced solid or mesh cover, a winch and cable system, and wall clips.
• Ice Expansion Protection: Heavy-duty air pillows (at least 4x4 or 4x5 feet) and an air pump.
• Plumbing Protection: Skimmer faceplate covers (like the Aquador), expansion plugs (winter bungs), and a non-toxic pool antifreeze if you have underground lines.
• Basic Tools: Screwdrivers, pliers, and a shop vacuum for clearing lines.

Estimated Project Benchmarks:

• Duration: 4 to 6 hours over two days (allowing for chemical circulation).
• Budget: $100 - $300 depending on the size of the pool and the quality of the cover.
• Prerequisite Knowledge: Understanding of basic water chemistry and the location of equipment drain plugs.

Systematic Execution of the Winterization Process

The following steps must be performed in sequence to ensure the pool is biologically stable and mechanically protected. Rushing the chemical balance or failing to drain the equipment properly are the primary causes of springtime "swamp" conditions or expensive hardware replacements.

Step 1: Deep Cleaning and Debris Removal

The presence of organic matter—leaves, insects, and pollen—during the winter months consumes sanitizer and provides a breeding ground for algae. Even if the water looks clear, microscopic spores and tannins from leaves can stain a vinyl liner permanently if left compressed under a cover for months.

1. Skim the Surface: Remove all floating debris using a fine-mesh net.
2. Brush the Walls and Floor: Use a nylon-bristled brush to scrub the waterline and any areas with low circulation, such as behind the ladder.
3. Vacuum the Floor: Perform a thorough vacuuming. If there is a significant amount of silt or algae, vacuum "to waste" if your multi-port valve allows it, to prevent clogging the filter during the final cleaning.
4. Remove Accessories: Take out the ladder, steps, and any over-the-wall skimmers or lights. Clean these items with a mild pool surface cleaner and store them in a dry, protected area.

Step 2: Precision Water Chemistry Balancing

Water chemistry behaves differently in cold, stagnant environments. Maintaining the proper saturation index prevents the water from becoming "hungry" (corrosive) or "saturated" (scaling).

1. Adjust Total Alkalinity (TA): Target 80–120 ppm. This acts as a buffer for your pH.
2. Adjust pH Levels: Set the pH between 7.2 and 7.6. If the pH is too high, your chlorine shock will be ineffective; if it is too low, the acidic water can cause the vinyl liner to become brittle.
3. Calcium Hardness: Maintain 200–400 ppm to prevent the water from leaching minerals from the pool's hardware.
4. Apply Winterizing Chemicals: Add a sequestering agent to prevent mineral staining, followed by a heavy dose of chlorine shock. Let the pump circulate these chemicals for at least 6 to 12 hours before moving to the next step.
5. Add Winter Algaecide: Once the chlorine level has returned to approximately 3 ppm, add a long-lasting winter algaecide.

Pro-Tip: Do not add algaecide and chlorine shock simultaneously. High chlorine levels can break down the active ingredients in many algaecides, rendering them useless for the winter.

Step 3: Lowering the Water Level and Skimmer Protection

How you handle the water level depends on whether you are using a skimmer cover plate or a traditional plug.

1. The Standard Method: Drain the water level to approximately 4 to 6 inches below the bottom of the skimmer opening and the return jets. This prevents water from entering the plumbing if the cover leaks or if there is heavy precipitation.
2. The Skimmer Faceplate Method: If you use a product like an "Aquador," you can keep the water at its normal operating level. You simply snap the plastic lid over the skimmer faceplate. This is beneficial for the pool’s structural integrity as it provides more internal pressure to counteract the weight of snow on the cover.
3. Warning: Never fully drain an above ground pool. The weight of the water is the only thing holding the pool walls in place. An empty pool can collapse or "blow away" in high winds.

Step 4: Draining and Storing the Filtration System

Water expands by approximately 9% when it freezes. Any water trapped inside a pump, filter, or pipe will exert enough pressure to crack heavy-duty plastic and cast iron.

1. Drain the Filter: Open the drain plug at the bottom of the filter tank. For sand filters, leave the plug off and set the Multi-Port Valve to "Winterize" or "Closed." For cartridge or DE filters, remove the elements, clean them thoroughly, and store them indoors.
2. Drain the Pump: Remove all drain plugs from the pump housing (usually there are two). Disconnect the pump entirely and store it in a garage or basement to prevent the motor seals from drying out and the internal components from rusting.
3. Clear the Lines: Use a shop vacuum on the "blow" setting to force any remaining water out of the return and suction hoses. Disconnect the hoses and store them to prevent them from cracking in the cold.

Step 5: The Air Pillow and Winter Cover Installation

The air pillow is the most misunderstood component of the closing process. Its purpose is not to support the cover, but to act as a "sacrificial" space. When water on top of the cover freezes, it expands inward. The pillow compresses, absorbing that pressure and preventing the ice from pushing outward against the pool walls.

1. Inflate the Pillow: Fill the air pillow to about 60–80% capacity. Do not over-inflate it, as it needs room to compress when the ice expands.
2. Center the Pillow: Tie the pillow in the center of the pool using thin nylon strings attached to the pool's top rails.
3. Deploy the Cover: Pull the winter cover over the pool and the air pillow. Ensure the cover is centered.
4. Secure the Cable: Thread the metal cable through the grommets of the cover and use the winch to tighten it securely under the top rail.
5. Wind Protection: In high-wind areas, use "wall clips" to snap the cover directly to the pool's uprights or use water bags (though water bags are more common for inground pools).

Warning: Do not use cinder blocks, bricks, or heavy weights to hold down the cover. If they fall into the pool, they will tear the liner and potentially cause structural damage to the floor.

Comparative Specifications for Winterization Materials

Choosing the right materials depends on your local climate and pool type. Use the following table to determine the optimal hardware for your winterization strategy.

Common Winterization Failures and Remedies

Even with a detailed plan, environmental factors can cause issues during the off-season. Recognizing these failures early can save the pool from catastrophic damage.

• Scenario: The Air Pillow Slips to One Side
  
  
  • Root Cause: Improper tethering or snapped strings during a windstorm.
  • Actionable Fix: Use a telescopic pole to reposition the pillow. For future closings, use a "center-cross" tethering method where four strings are tied to the pillow and secured to four equidistant points on the pool frame.
• Scenario: Excessive Water Accumulation on the Cover
  
  
  • Root Cause: Heavy rainfall or melting snow creating a "sump" effect that pulls the cover into the pool.
  • Actionable Fix: Use a specialized submersible cover pump to remove water once it reaches a depth of 2 inches. This reduces the stress on the pool walls and prevents the cable from snapping.
• Scenario: The Cover Sinks into the Pool
  
  
  • Root Cause: Loss of water level beneath the cover due to a liner leak or a failure in the cable/winch system.
  • Actionable Fix: Immediately inspect the water level. If the water level is dropping, you have a leak that must be patched even in winter. If the water level is fine, re-tighten the cable or replace the winch.
• Scenario: Visible Algae Growth Under the Cover in Early Spring
  
  
  • Root Cause: Closing the pool while the water was too warm (above 65F) or using an old, porous mesh cover.
  • Actionable Fix: Peel back a corner of the cover and add a "boost" of liquid chlorine or a fast-dissolving algaecide four weeks before you plan to officially open the pool.

Frequently Asked Questions

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

You should close the pool once the water temperature is consistently below 65°F (18°C). Closing too early while the water is warm provides a perfect environment for algae to bloom under the cover, while closing too late risks sudden frost damage to your pump and plumbing.

Do I really need an air pillow for an above ground pool?

Yes, an air pillow is essential for above ground pools in regions where the water freezes. It creates a "void" in the ice sheet, forcing the ice to expand inward against the pillow rather than outward against the pool walls, which could otherwise cause the pool to "ice-split" or collapse.

Can I leave my pump and filter outside during the winter?

While you can leave the filter tank outside if it is fully drained, it is highly recommended to move the pump motor indoors. Cold temperatures and moisture can degrade the motor windings and gaskets, leading to a failure or "frozen" motor when you attempt to start it in the spring.

How much should I drain my pool for the winter?

If you are not using a skimmer cover plate, drain the water to about 4-6 inches below the skimmer. If you are using a skimmer plate like an Aquador, you do not need to drain the water at all, provided you have protected the return lines with expansion plugs.

Should I use a cover pump?

A cover pump is highly recommended for solid covers. Removing excess rainwater and snowmelt prevents the weight from pulling the pool walls inward and makes it much easier to remove the cover in the spring without dumping dirty water back into the clean pool.

Secure Your Investment for the Spring

Following this rigorous winterization protocol ensures that your above ground pool remains a source of relaxation rather than a structural liability. By focusing on chemical balance and mechanical protection now, you guarantee a simplified, cost-effective opening when the swimming season returns.