The Best Way to Close a Swimming Pool

The Best Way to Winterize a Swimming Pool
by Rob Cox August 23, 2018

The Best Way to Winterize a Swimming Pool

winterize a swimming pool

Every swimming pool is different - different surfaces, sizes, shapes, filtration, heating and purification equipment. Winterizing a pool also has slight differences in procedure, depending on the equipment. That said, you'll still be doing essentially doing the same thing.

If you're new to pool winterization, it involves removing the water from the underground pipes and the above ground equipment, and then cleaning, adding chemicals, and covering the pool. That much is the same for all pools, but there are other basic principles that apply to all pools, big and small.

PRO TIP: For best results, winterize before the first frost  



Balance the pool water one week before closing. If you try to dump in 3-5 different chemicals within an hour, they may not adjust to desired levels, and there won't be enough circulation to disperse the chemicals very well. This can damage your pool surfaces and lead to bad winter water quality. The best way to do it is to test and adjust the water a week prior to closing, and then test again just before you add your winter chemicals.

Shock the pool water 5-7 days before closing. This should be done after balancing the water, but several days before adding your winter chemicals and closing the pool. When pool shock is added to the pool at the same time as other chemicals, all sort of interference can happen. What usually happens in the case of pool closing is that the shock will interfere with other important winter pool chemicals, such as algaecide and stain/scale products. Make sure sanitizer levels return to normal before attempting to add winter chemicals.

Add the sequestering agent and/or enzymes 24 hours before closing. A stain and scale preventer should be used if you have a salt pool, high calcium hardness levels or metals in your water. Enzymes are great for pools in dusty rural or smoggy urban areas, or for mesh covered pools that tend to open up green. For best activation, these products both need to be circulated by the filter pump for at least 8 hours prior to closing.


1) Clean the pool. Brush, vacuum and skim the entire swimming pool so it's spotless. Also clean up around the pool deck.

2) Clean the filter. If you have a sand or DE pool filter, backwash the filter thoroughly (about 10 minutes). Remove DE grids and filter cartridges and hose them off completely. After cleaning, store grids or cartridges inside filter tank, and secure filter clamp band tightly.

3) Lower the water level. You can do this by using the filter pump, a cover pump or siphon it out using the vacuum hose. Vinyl pools can use snap-on skimmer covers to close the pool without lowering the water level. Here are the guidelines for lowering the water level in your pool:

3) Add winter algaecide. Use a quality product that's built to last through the winter, such as Poly 60. Disperse the algaecide by walking it around the pool. Dosage = 16 oz. per 10,000 gallons.

4) Add the chemical floater. Use a heavy duty winter floater filled with chlorine tablets or other winter sanitizer, and tie it off with a long piece to twine on both sides of the pool. This will keep it stationary and prevent damage to pool surfaces.

5) Blow out the plumbing lines. While the blower is still going, plug the wall fittings to keep the water from coming back in.

  • Blow out the lines with a Cyclone, a small compressor or a large wet/dry vac.
  • Put the air in at the skimmer or the pool pump to force air through all the lines and equipment.
  • Plug the lines tightly (skimmers, wall returns, cleaner lines, spa jets) with specialized pool plugs to keep water out.
  • Remove all drain plugs from equipment, and store them in the pump basket with the pressure gauge.

6) Winterize skimmers. A skimmer guard will absorb ice expansion from water inside the skimmer and prevent it from cracking. You can also make your own skimmer guard with a (clean) quart-sized plastic bottle half full of non-toxic pool antifreeze or small pebbles.

7) Cover the pool. The winter pool cover or safety cover should be tightly secured. Covers keep out leaves and debris, and are made to withstand strong winds and heavy winter weather.

  • Above ground pools should use an air pillow to break up the ice sheet that forms across the pool.
  • Covers on above ground pools can be protected from high winds with items like cover clips, a cover seal or wall bags.
  • Above ground filter systems and hoses can be moved indoors, but inground systems usually stay outdoors. 



  • Busted pool lines: Make sure all the water is out of the plumbing and equipment and be certain the lines are plugged. When in doubt, add pool antifreeze as a back-up measure.
  • Bad water chemistry: Balance your pool water a week before closing, and shock the water 5-7 days before closing.
  • Pool opening problems: Cover the pool when spotlessly clean to prevent stains and conserve chemicals.
  • Pool cover falls in or flies off: Secure the winter pool cover as best as possible to prepare for the worst winter weather.
  • Pool equipment damage: Don't forget to shut off power to the pump at the breaker. Not doing so could result in accidentally running a dry pump, which will leave you looking for replacement parts...or possibly a new pool pump!