How to Winterize Your Pool

Before you shock the pool, you must establish a strong chemical foundation. Balanced water is less likely to corrode equipment or damage the pool structure over winter. Test all four parameters using a quality test kit. For detailed testing guidance, see our complete pool water testing guide.

Target pH between 7.2-7.6 to prevent metal corrosion and plaster etching. Alkalinity should be 80-120 ppm to stabilize pH and prevent chemical swings. Calcium hardness needs 200-400 ppm to avoid plaster deterioration and scaling. Finally, chlorine should be 1-3 ppm before shocking. Wait 2-4 hours after adjustments for circulation before moving to step 2. Proper chemistry now means less stress on pool surfaces and equipment during months of dormancy. Use our dosage calculator to determine exact chemical amounts for your pool size.

Remove all debris, dirt, and algae before adding winter chemicals. A dirty pool wastes chemicals and increases staining risk. Brush walls and floor thoroughly using 45-degree strokes on plaster surfaces to remove algae spores and buildup with a quality pool brush. Vacuum the entire pool floor using the main drain if available to pull debris faster.

Clean the tile line with a brush and mild acid solution to remove buildup that promotes algae growth. Empty all skimmer baskets and check the pump basket for debris. Use a non-abrasive sponge to clean the waterline, and run circulation for 2-4 hours after brushing to send debris through the filter. A clean pool takes 20-40% less chemical and is significantly easier to maintain next spring.

A strong chemical dose creates a protective barrier that lasts through winter. Add 2x the normal shock dose of cal-hypo shock (check instructions for your pool size). For example, if normal is 1 lb per 10,000 gallons, add 2 lbs per 10,000. This kills remaining algae spores and oxidizes organic matter. Use our shock calculator to determine exact dosages. Let it circulate overnight before adding the next chemical.

Twelve to twenty-four hours after shock, add winter algaecide (copper-free preferred) at label rates. Copper-based algaecides can stain pool surfaces (especially plaster) when left sitting in stagnant, uncirculated water for months. Always use a copper-free formula for winterization. Winter formula is designed for colder temperatures where regular algaecide may not work effectively. Then add stain and scale preventer at label rates to protect plaster from mineral staining and metal oxidation. Finally, consider enzyme treatment per label instructions—it breaks down organic buildup and helps spring opening go faster. Always follow this sequence: shock first, wait 24 hours, then algaecide, then stain preventer. Adding them simultaneously can cause chemical reactions.

Lowering water prevents ice from building up and pushing on equipment or pool walls. But how much you lower depends on your pool type. For concrete and plaster pools, drain water to 6 inches below the skimmer opening. This ensures the skimmer and return lines are above water level, preventing ice from freezing inside lines and causing cracking. For vinyl liner pools, lower water 4–6 inches below the skimmer opening, ensuring the liner remains fully supported by water. Lowering too far risks liner shrinkage and stress, especially in cold weather when vinyl becomes less flexible.

Use a submersible pump for the fastest drainage, positioning it in the deep end and running discharge to an approved drain location. Our pool volume calculator helps determine how many gallons you'll be draining. Alternatively, use your main drain valve if the system has one, though this is slower. Never drain completely unless directed by a professional for major repairs—exposed pool walls are highly vulnerable to freeze-thaw damage.

This is the most critical step. Water trapped in lines freezes and expands approximately 9%, cracking pipes and causing catastrophic damage: cracked pump casings ($500-$1,500), broken pipes ($2,000-$5,000), damaged filter tanks ($1,000-$3,000), and ruined heaters ($2,000-$8,000). Invest 30 minutes now to avoid $5,000+ in spring repairs. See our pool filter guide for more on protecting your equipment.

Turn off the pump completely and close the main drain valve to force air through suction lines. Open the skimmer line isolation valve. Connect an air compressor or shop vac to the line using a threaded blow-out adapter. Start at 20 PSI and gradually increase to 40-50 PSI, never exceeding 60 PSI to avoid blowing out gaskets. Listen for whooshing sounds and watch for water spray from return openings in the pool. Keep the compressor running 30-45 seconds after water stops flowing to ensure NO water remains in the line.

Immediately install an expansion plug while air is still flowing—do not wait, as water will trickle back in. Repeat for EACH suction and return line. Most pools have 2-4 return lines. After blowing out, drain the pump, filter, heater, and chlorinator completely. Finally, pour pool antifreeze (RV/pool grade, NOT automotive) down return lines after plugging for extra protection—typically 1-2 quarts per line per label instructions. Consult our equipment troubleshooter if you encounter issues during the blow-out.

Exposure to freezing temperatures and moisture damages pumps, filters, and electronics. Remove portable equipment like ladders, handrails, eyeball fittings, return covers, test probes, robotic cleaners, suction-side cleaners (Kreepy Krauly, etc.), and pressure-side cleaners (Polaris)—store them indoors. Drain all water from robotic cleaners and store indoors — freezing temperatures will destroy internal motors and components. Remove and drain large equipment: pump and motor should have the breaker turned off, drain plug opened, and plastic sheeting cover applied. Place all drain plugs inside the pump strainer basket so you can find them easily in spring — this classic pro tip saves many frantic searches. Filter tanks must be drained completely with the top open and covered with plywood or tarp.

If you have a pool heater, close isolation valves and open the drain plug. If removable, store it indoors. For salt systems, remove the salt cell and store indoors—warranty voids if left outside. Use a dry, temperature-controlled garage or shed for storage. Don't stack items as this causes warping. Label everything with photos of electrical connections before disconnecting to ensure easy reassembly. Hang hoses to dry completely before storing to prevent mold growth. Never store chemicals indoors as they react dangerously with moisture and temperature changes.

A proper cover protects water from debris, reduces evaporation, and keeps out light that feeds algae. A loose or damaged cover defeats the entire purpose. Clean the pool deck thoroughly first—any sharp objects, sticks, or dirt will puncture the cover. Position the cover at one end with the seam running lengthwise. Have a helper ready to assist as you unroll and center it slowly across the water. Use a cover roller or winch if available for even distribution.

Install water tubes or air pillows along the underside perimeter, spacing them every 3-4 feet to hold the cover against wind. Secure with cables and winch (or manual straps), tightening evenly around the perimeter. The cover should be snug but not overstressed. If using a solid cover, install a thermostat-activated cover pump to remove rain and snow water that collects on top—idle pumps can freeze and break. Check for gaps or sags. The cover should be tight and level, as sagging areas collect water and debris. During winter, remove heavy snow after storms (more than 12 inches puts dangerous stress on structure), keep the cover pump running, and check cable tension monthly as winter winds loosen them.