A DIY Guide to Winterizing a Swimming Pool

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Unless you are lucky enough to live in a tropical climate where a swimming pool is used year-round, winterizing a swimming pool will be necessary before you can let it sit idle for the months it is inactive. The idle period may be only a few weeks in places like Arizona or Alabama, or it may be six months or more if you live in a northern climate like Minnesota or Maine. Either way, there will be a winterization routine to go through on an annual basis.

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Winterizing a pool is usually done to prevent damage to the pool and pump caused by freezing temperatures, but it may also be done simply to protect the pool if you happen to be leaving home for an extended period. In a southern climate, for example, you may well winterize the pool if you are leaving for vacation even if freezing temperatures aren't an issue.

When to Winterize a Pool

As soon as you stop using your pool for the season, it is generally time to begin thinking about winterizing it. For many homeowners, Labor Day weekend marks the time for winterizing the pool, but this will vary depending on where you live. In any case, you want the winterizing routine to be done well before temperatures begin to dip to 32 degrees Fahrenheit or below. If you have an unseasonable cold snap before you've winterized the pool, you can prevent freezing by leaving the filter pump running since running water is unlikely to freeze. In any case, it is wise to have the pool winterized and covered by October or Thanksgiving at the latest.

How to Winterize a Pool

The details on how to winterize a pool vary slightly for in-ground pools and above-ground pools, but the basic procedure is the same.

Step 1: Clean the Pool

Your pool will weather the winter better if it's as clean as possible before you cover it. This involves several different steps: scrubbing away any visible stains or algae from the walls of the pool, using a leaf net or hand skimmer to remove as much debris as you can, running the automated cleaner (if you have one) over the bottom of the pool and then removing it and putting it away and finally running the pool filter for an extended period to clean the water as thoroughly as possible.

Step 2: Lower the Water

The next step is to drain water from the pool to the level recommended by the pump manufacturer. This often means the water level should be about 1 foot below the level of the skimmer but always follow the recommendations of the pump manufacturer. The cover manufacturer may also provide instructions on the proper water level for the winter period.

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Step 3: Test and Balance the Water

Now it's time to test and adjust the pH and chemical levels of the water using the same test kit used to maintain your pool through the season. Some experts recommend setting the chemical levels slightly higher for the winter since the levels will drop slightly over the winter.

The pH levels should typically be in the range of 7.4 to 7.6. Optimal chemical levels are:

  • Chlorine: 1.0 to 3.0 ppm
  • Total alkalinity: 80 to 140 ppm
  • Calcium hardness: 200 to 400
  • Chlorine level: 5 ppm and below

Step 4: Add Winterizing Chemicals

If it's recommended by the manufacturer of the filter system, add winterizing chemicals to your pool. Sometimes sold as "pool-closing kits," these chemicals will keep the pool protected and the walls of the pool clean over the winter. Some kits use slow-dissolve floaters that gradually release chemicals over several months. Some winterizing kits recommend shocking the pool by adding a burst of chemicals to protect against algae growth in the winter. This step should be done right before covering the pool.

Step 5: Clean the Pool Filter

Follow the manufacturer's instructions to clean the filters and water lines of your pump system. With cartridge filters, this is usually just a matter of removing and cleaning the cartridge and connector hoses and storing them. Diatomaceous earth and sand filters can be a little more complicated, so follow the manufacturer's instructions for whatever backwashing is recommended. You should also drain booster pumps, chlorinators or other components that are part of the system.

Step 6: Blow Out Water Lines

Fully removing all water from the pump lines is a good idea, especially if you live in a climate where freezing winter temperatures are likely. This can be done with an air compressor or sometimes even with a powerful wet-dry shop vac. Be thorough with this step and remove as much water as possible from all components of the pump and water lines.

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Step 7: Remove/ Replace Drain Plugs

Remove all the drain plugs from the pump system. If you wish, you can store these in the skimmer basket and put them away in a safe place. The drain plugs may be a little tricky to find, so refer to the pump instructions to locate them.

If recommended, replace the drain plugs with special expansion plugs, sometimes called "winterizing plugs." These are expandable plugs designed to prevent damage from freezing water, and their use is recommended in regions with frigid winters. In regions with especially cold winters, the pump manufacturer may also recommend adding a pool antifreeze to the pump lines.

Step 8: Shut Off the Power

Make sure the pool pump is disconnected from electrical power to prevent accidental startup that can damage the pump if it operates without water in the system. This can be done by simply shutting off the circuit breaker controlling the pump. It's also a good idea to clear the pump timer so that if the breaker is inadvertently turned on, the pump won't run.

Step 9: Remove Deck Equipment

Most people like to remove any miscellaneous equipment attached to the pool, including rails, skimmer baskets, eye fittings, ropes, ladders and diving boards. Store everything where it will be protected from winter weather.

Step 10: Cover the Pool

The last step is to cover the pool for the winter. This will prevent debris from falling into the pool and will also protect the pool from sunlight and algae. Covering the pool will also help keep the water chemistry more stable. Make sure the pool cover is in good condition without any tears or holes. Minor damage can be patched with repair tape.

If you live in an area where snowfall is likely, it's a good idea to place inflatable air pillows in the center of the pool before covering it. The pillow will support the center of the cover and lessen the stress on it if snow piles up.

If you want to use water bags to hold down the pool cover, make sure to fill these only 1/2 to 3/4 full for the winter. This will prevent them from breaking should cold temperatures freeze and expand the water inside them.

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Winterizing Above-Ground Pools

Permanent above-ground pools are winterized using the same steps as for in-ground pools except that all the above-ground water lines must be removed and stored for the winter. Make sure the water lines are drained of all water before you store them in a dry location.

A portable above-ground pool must be fully drained before you disassemble it and roll up the liner. Make sure the water is correctly balanced before draining so it won't damage the environment. Make sure the liner is completely dried off and then roll it up and store it in a dry location.

Winterizing Saltwater Pools

Saltwater pools are winterized in much the same way as freshwater pools, but there is one critical difference. After lowering the water level, turn off all the equipment and then disconnect and remove the salt-generator cell. Clean out the cell and store it. Then, continue with the other steps for winterization.

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Bryan Trandem is an avid home improvement DIYer and trained Master Gardener. He has been writing and editing books and articles on gardening, home improvement, woodworking, and home decor for more than 30 years. He lives in Minneapolis, MN.