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Tough to believe — Winter is coming!


By Marcelle Dibrell

September through November are busy months for service professionals. Following the summer months, pool owners start thinking about preparing their pools for the freezing temperatures that can damage equipment, interior finishes, plumbing, tile and structures. For those who live in climates that experience significant seasonal variation, it is essential to protect pools to minimize and prevent both physical and chemical damage to components of the pool. Closing should occur before the first hard freeze.

The methods used in closing down a pool vary from region to region. The timing of maintenance and services that are performed on an individual pool are often dictated by local climate conditions and customs. However, most winterizing procedures share several common features that can be used to protect pools regardless of the type of interior finish and structure. How much is involved in winterizing a pool depends on many factors. For example, the expected temperature range, the amount of precipitation and the depth of the frost line all dictate what must be done to avoid damaging surfaces and equipment.

All equipment should be serviced in accordance with the manufacturer’s instructions. The following is a general guideline - based on the Association of Pool and Spa Professionals 4th edition Service Technician Manual - of basic steps to take.

Water care

Most winterizing processes begin by balancing the pool water to APSP standards. As the water temperature decreases, the Langelier Saturation Index (LSI) will also decrease, meaning that water will become more corrosive. The water should be balanced 3-7 days prior to closing the pool, and then be adjusted, and rechecked prior to covering the pool.

Look for the APSP recommended water quality parameters at the end of this story.

To compensate for the downward LSI drift, it may be desirable to balance the water in a positive range.

It is recommended to shock chlorine and bromine pools, kill bacteria and algae, and remove other organic contaminants such as bather waste from the water. Allow chlorine residuals to drop to reasonable levels before adding additional closing chemicals such as algaecides and sequestering agents that may be degraded by high levels of oxidizer.

Biguanide sanitized pools should be oxidized with hydrogen peroxide.

It is a good idea to add an EPA registered algecide, because of the lack of water filtration and certain types of covers that allow sunlight, fine organic debris and contaminants to enter the pool water.

To prevent staining to interior finishes, use an appropriate stain preventative. Winterizing kits contain sequestering or chelating agents for this purpose. After adding winterizing chemicals, follow label instructions for the disposal of any remaining chemicals.

As with all chemical application to pool water, proper safety considerations must be followed.

Do not mix chemicals. Follow manufacturer’s directions for the proper use of chemicals including the correct time to add winterizing chemicals to avoid damaging surfaces, covers and equipment.

Thoroughly clean the pool. Brush off all surfaces including walls, coves and floor. Remove any floating leaves and other organic debris.

Vacuum the pool. Equipment

Next, clean the filter. Backwash a sand filter several times. For cartridge filters, remove and clean the cartridges, and allow them to dry. DE grids should also be removed and cleaned. Store cartridges of grids for the winter in a warm dry indoor location.

It is not recommended to clean DE grids and cartridge filters with muriatic acid solutions and then store them for the winter. The acidic residual may stay in the grids or cartridges and degrade them while in storage. After any acid rinse, rinse thoroughly with water to remove any acid residue and allow to dry completely before storage.

Empty all chemical feeders.

When cleaning out chemical feeders, exercise caution and wear the proper safety equipment such as gloves and safety goggles. Check with the manufacturer regarding disposal of chemicals from feeders.

Disconnect the power to automated controllers and chemical feed equipment. Remove any sensors from the flow cells, then clean and store them as per the manufacturer’s directions. Empty and clean the flow cells and allow them to dry prior to storage.

If there is a peristaltic pump in use, remove and clean the feed and injection tube. Allow it to dry before storage.

If the automatic controllers are installed outdoors, they should be removed and stored indoors or elsewhere for protection from extreme weather.

For pools that use an electrolytic chlorine generator, drain any water in the cell and then remove the cell and store indoors.

Drain the pump, filter and heater. Place the drain plugs in the hair and lint basket, so that they are easy to locate in the spring.

Purge any remaining water from the pump, heater, heat pumps and other wet equipment. Pool equipment and lines cannot take excessive pressure and overpressure could present a safety hazard; care should be taken to use the proper procedures and equipment (e.g. wet/dry shop vacuum, low pressure air compressor, etc.). Only trained professionals familiar with the potential hazards associated with pressurized air should perform this process.

Disconnect electrical power to any heaters or heat pumps and ensure the circuit breakers are in the “off” position. The pilot flame should be turned off, as well as the main gas valve and gas supply to the gas heater. The heat exchanger should be drained as per the manufacturer’s directions.

Circuit breakers should be in the “off” position. Remove and store pump motors indoors in a dry location. Motors that are left outdoors should have a weatherproof cover.


Plumbing lines must be protected from the freezing of water within the lines. Purge water from these lines with an air compressor or the discharge side of a shop vacuum. Purge all return lines, suction lines (skimmer and main drain) and lines to water features, solar heating, pool cleaners and slides.

Once the return lines are clear of water, remove the wall fittings and insert tapered expandable plugs. It may be necessary to use straight pressure plugs in some locations.

Blow air through the suction outlet (main drain) lines and plug the pipe topside or close the valve to the suction outlet.

Purge skimmer lines with air and screw in a threaded expansion plug into the skimmer. This will prevent freezing water from cracking the skimmer. To ensure a water tight seal, use an appropriate (e.g. PTFE) plumbing tape on the threaded fitting.

Many service techs dislike using antifreeze in the winterizing process. However, if antifreeze is used, never use ethylene glycol based (common automotive) antifreeze in winterizing pool equipment and plumbing lines. Always use a pool formula antifreeze or a propylene glycol based product. Antifreeze should be used sparingly to avoid problems when opening the pool in the spring.


Water should be drained from the pool based on regional differences and the type of cover (solid or mesh) used on the pool. To avoid damaging the cover, consult the cover manufacturers for the proper amount of water to be drained. Freezing surface water can damage waterline tiles and expose plaster surfaces to the atmosphere, which can create cracking and defined water line indications on the surface.

The APSP’s 4th edition Service Tech Manuel provides guidelines for different types of pools and the suggested drain down levels as follows: 1. Vinyl Lined: 1 inch (25 mm) below the skimmermouthortileline,whicheverislower.

2.Plasterfinisheswithsolidmaterialcover: 1-6 inches (25-152 mm) below the skimmer mouth or tile line, whichever is lower.

3. Painted or natural finish with solid material cover: 6 inches (152 mm) below the skimmer mouth.

4.Withnocoverormeshcover:18-24inches (457-610 mm) below the skimmer mouth.

5. WithAutomatic Cover: water should be nolowerthanthebottomoftheskimmermouth.

Remove and clean ladders, diving boards and handrails. Store in a dry place.

The four main types of winterizing covers are described in Chapter 10-3 of the 4th edition APSP’s Service Tech Manual: 1. Solid Lightweight Fabric Cover: Constructed of a solid film or sheet of synthetic fabric, held down by water tubes, sandbags, or ropes and anchors. *Note: Avoid overfilling water tubes that are used to anchor some types of covers to avoid splitting the tubes during freezes. Do not use masonry blocks, bricks or concrete stepping pads to hold down covers as they could fall in the pool and damage the interior finish of the pool.

2. Spring-loaded ASTM Mesh Safety Cover: Made of mesh fabric, usually anchored to the pool deck.

3. Spring-loaded ASTM Solid Safety Cover: Made from reinforced vinyl fabric, usually anchored to the pool deck.

4. Automatic and Manual Safety Covers with Tracks: Made of solid fabric, available in standard and custom sizes.


Leaves and other organic debris should be removed from all covers to prevent plugging the cover pump or damaging the cover.

Solid covers should have automatic cover pumps to remove water from rain or melted snow to avoid a safety hazard.

Monitor tracked solid covers for accumulation of water, snow and ice. Excess weight from precipitation can damage the track system and also possibly damage the concrete, coping or pool wall.

Long term durability and longevity of a cover depends on proper water balance, proper water levels under the cover, and regular maintenance and cleaning.

WARNING: All solid safety covers must meet ASTM F1346-91 (2010), “Standard performance specification for safety covers and labeling requirements for swimming pools, spas and hot tubs” and have an automatic means of preventing water accumulation on top of the cover whenever the pool is covered. For example, this may be accomplished with a drain panel or a pump. Rain water on the cover is a drowning hazard for children.

Inform consumers of the necessity of preventing wateraccumulationontopofthecover. Cover a pool only when the water analysis indicates the chemical parameters are within the cover manufacturer’s recommended ranges.

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