Clean out the pool.
The first step is to clean out any leaves, insects, dirt and debris. Use your pool vacuum, or just fish them out with a net. Clean out the skimmer and the pump basket, too.
Clean the tile line with tile cleaner. Easier now than next spring, when the scum has had all winter to set.
Balance the water chemistry.
This protects the pool from corrosion or scale buildup. Using a water test kit, adjust the water to the recommended levels of pH, total alkalinity, calcium (hardness) and chlorination.
If you want to add a winterization chemical kit, do it now. These kits put high levels of chlorine and algaecide in the water to prepare it for the winter months ahead. Your pool retailer offers ready-made kits for the purpose; use according to the maker's directions. In the case of larger pools, you may be directed to supplement the kit with additional quantities of some chemicals, too.
Don't let your chemicals damage your pool.
Don't add tablets or a floater that contains chlorine or bromine—they can damage the equipment nearest them. If you already have chlorine or bromine tablets in your feeder, let them run out so that none remain. If you're adding winterizing chemicals, pour them into a bucket and then into the pool. Some of these chemicals instruct you to turn on the pool filter while you add the chemicals. Make sure you do, especially if you have a vinyl liner pool—you don't want stains on your liner from un-dissolved granules or damage to your equipment from concentrations of chemicals in the water.
The #1 enemy: freezing.
When water freezes, it expands with enormous force. It's the force that breaks up highways, splits garden hoses, explodes beverage cans in your freezer, and it's the force that expands and cracks pool pipes, filters, pumps and skimmer baskets. If you are closing up your pool for the winter, you should always take precautions to protect from freeze damage no matter where you live—even pool owners in the South have learned, to their regret, that freezing temperatures are an ever-present risk.
To start the process, drain the water down below the skimmer mouth. DO NOT EMPTY THE POOL! The expansion of the soil under the pool as the water in the soil freezes can jack the pool right out of the ground; it needs the weight of some water to keep it firmly in place.
Be good to your pump and heater.
Disconnect your pump and filter. Make sure all water is completely drained from the pump. For insurance, turn it upside down once and dump any excess water out. Remove the drain plugs from it (there may be one or two); they'd trap water inside, which is bad. Once you've drained the pump, turn it on for just a second or two (no more—the seal is vulnerable to damage) to expel any remaining water from the impeller. Store any small plugs or parts in the pump basket, so they're easy to find next year.
If you have a heater, drain it and make sure there is no standing water inside. Blow it out with a compressor or shop vac. Drain the heater completely, remove any drain plugs, and stash those plugs too in the pump basket for next season.
Remove all return jet fittings (the entire fitting!). If you crack a fitting while removing it, don't panic! You can get a replacement come spring. Remove all skimmer baskets. Put fittings and any other items that you remove in one of the skimmer baskets or the pump basket to avoid loss (this includes the dive board bolts too).
No water in the pipes = no freeze damage.
Unscrew and loosen any quick-disconnect fittings or unions at your pump and filter system, then blow out the pipes. A wet-dry shop vacuum or air compressor is ideal for this. Force the air from your pump down the skimmer and through the skimmer (or "suction side") pipes.
Blow out the return plumbing by hooking up your compressor to the return lines at the filter system, or by screwing it into the pump's drain plug. Keep at it until you see air bubbles emerge from the return jets, then tightly plug the fitting below the water line. Close up all exposed pipes with plugs.
Also blow out the main drain line (if any). No diving necessary to plug up the drain pipe—when you see bubbles coming out of the drain, plug the pipe on your end or close the gate valve. This will create an "air lock" in the line, ensuring that no more water can enter it from the pool side, which protects the main drain line.
Clean the filter.
Remove the filter hoses. Spray the cartridge filter elements and D.E. (diatomaceous earth) grids with Filter Cleaner, then rinse them clean with a garden hose. For D.E. filters, drain the filter tanks and leave the backwash valve open. If you have a sand filter, clean it by backwashing.
Important: Don't acid wash a D.E. filter at pool closing time. Wait until spring, when you can conveniently run pool water through the system to rinse it out. Simply rinsing off the acid and putting away the filter will give the acid all winter to attack the filter components.
Open the drain at the bottom of the filter to let out any water in the filter outlet; be sure to open the air relief valve on top if you have one. Put the multiport valve in the closed or "winter" position—blow the water out of it if necessary—and remove the pressure gauge. Stow the drain plug with the other removed items you're stashed in the pump basket.
Your final freeze insurance: the flotation device.
Before you put on the cover, you'll want to install a flotation device in the center of the pool. This device needn't be anything fancy—it can be a "pillow" sold at your local pool retailer or a truck innertube. The float balances the rainwater and ice sure to form on your pool's cover over the winter. Even more important, it eases pressure on the pool walls by allowing winter's ice to push in on the flotation device, not outward on the walls.
Last step: The winter cover.
The winter cover is important for both the pool and the people around it. It's stronger than a summer cover, both to withstand the weight of snow and ice, and to protect people or pets from accidentally falling through the cover into the water.
If your cover has any rips, fix them. If they're beyond repair, replace the cover. Stretch the cover over the pool, black side down. If any sharp points are protruding from beneath, cushion them with cardboard or rags. Then stretch the cover very tightly across the pool (this can be a 2-3 person job). Run a strong wire through the holes around the perimeter of the cover, and snug it up using a wrench so the cover stays down in winter's winds and rains.
Time for storage.
Remove rope and floats from pool and put with the rest of the supplies. Store any dive board and ladders in the shed or garage, with your pump and filter. Store your dive bolts or ladder bumpers in the pump basket. If you have a sand filter, just leave it outside.
Your pool is ready for winter's worst. Your investment is protected. And your spring pool opening should be an easy step to another season of swimming enjoyment!