Why Proper Winterization Matters
Closing your pool for winter isn't just about covering it and walking away. Water expands when it freezes, and if it's trapped inside pipes, equipment, or the pool shell itself, the pressure can crack pipes, damage pumps, split filter tanks, and heave pool walls. A properly winterized pool avoids all of this — and reopens cleanly in spring without the need for extensive remediation.
This guide covers the full winterization process for in-ground pools in climates that experience freezing temperatures.
When to Close Your Pool
The ideal time to close is when your local air temperature consistently drops below 65°F (18°C). Closing too early while it's still warm encourages algae growth under the cover. Closing too late risks a freeze event catching you unprepared.
Step 1: Balance Your Water Chemistry
One to two weeks before closing, balance the water to these targets:
- pH: 7.2–7.6
- Total Alkalinity: 80–120 ppm
- Calcium Hardness: 175–225 ppm
- Free Chlorine: 1–3 ppm
Properly balanced water at closing prevents corrosion and staining over the winter months when you won't be monitoring it.
Step 2: Clean the Pool Thoroughly
Close a clean pool. Brush the walls and floor, vacuum thoroughly, and skim the surface. Remove all visible debris. Leaving organic matter in the pool over winter fuels algae growth and stains surfaces.
Step 3: Shock and Add Winter Chemicals
The night before closing:
- Shock the pool with a double or triple dose of chlorine shock. Allow the chlorine to drop back below 5 ppm before adding the winter algaecide.
- Add a winter algaecide — specifically formulated for slow-release over several months.
- Add a winterizing enzyme product if available — breaks down organic contaminants over winter.
- For areas with very cold winters, consider adding a metal sequestrant to prevent iron and copper staining.
Step 4: Lower the Water Level
Lower the water level to below the skimmer and return jets:
- Mesh cover: Lower to about 12–18 inches below the coping
- Solid cover: Lower to about 6 inches below the skimmer mouth
This prevents water from sitting in the skimmer, which can crack when frozen.
Step 5: Blow Out and Plug the Lines
This is the most critical step. All water must be removed from the plumbing lines before a freeze. Use a shop vac or an air compressor to blow out water from every line — skimmer lines, return lines, main drain line, and any auxiliary lines for features or cleaner ports.
Once each line is blown clear, plug it with an expansion plug (for return jets) and a Gizzmo or similar device (for skimmer lines) to absorb any residual ice expansion.
Step 6: Winterize All Equipment
- Filter: Backwash or clean the filter. Remove the drain plug. For cartridge filters, remove and store cartridges indoors.
- Pump: Remove drain plugs. Store them in the pump basket for safekeeping. Remove and dry out any O-rings; lightly lubricate and store them.
- Heater: Refer to your manufacturer's instructions. Drain all water. Turn off the gas supply.
- Chemical feeders / chlorinators: Empty and clean. Do not store with chlorine tablets still inside.
- Lights: Verify they're sealed. Water in the light housing can cause issues.
Step 7: Install the Winter Cover
A quality cover protects the pool from debris, sunlight, and evaporation. Secure it firmly — loose covers can sag into the water or blow off. Use water bags or cover anchors around the perimeter. For solid covers, a cover pump is essential to remove rainwater accumulation throughout winter.
Step 8: Store Equipment Properly
Store any removable equipment — ladders, rails, diving boards, slides — in a dry, protected location. Clean them before storing to prevent staining or corrosion.
One Final Check
Walk around the pool and visually inspect everything. Plugs in? Cover secured? Pump and filter drained? Equipment stored? A five-minute final walkthrough every closing day is the cheapest insurance you can get.