Pool Winterizing Checklist (US Climates)

Closing your pool right is the cheapest insurance you'll ever buy. A proper close costs ~$50 in chemicals and one afternoon; a bad close costs a cracked pump, stained plaster and a green swamp in April.

Step 1 — Fix the water BEFORE closing (week of closing)

• pH: 7.4–7.6 — the number your water sits at for months
• Total alkalinity: 80–120 ppm — buffers the water all winter
• Calcium hardness: 200–400 ppm (lower for vinyl) — protects plaster from etching
• Chlorine: shock to 10+ ppm the day you close — this is your winter algae defense
• CYA: 30–50 ppm if using an algaecide-free winter kit
• Run the pump 24 hours after adding closing chemicals before shutting down

Need exact doses? Chlorine calculator · Alkalinity calculator · Calcium calculator — all work for closing doses.

Step 2 — The closing sequence

• 1. Deep clean: vacuum, brush, empty all baskets. Organic matter left in = stains by spring
• 2. Backwash/drain equipment: filter, pump, heater, chlorinator — every drain plug open. Water left inside cracks housings at 28°F
• 3. Blow the lines: shop-vac or blower on the return/skimmer lines, then plug them with winterizing plugs. Above the freeze line in mild climates, some owners just lower the water below the skimmer instead
• 4. Add winter chemicals per step 1, through the deepest return with the pump's last circulation
• 5. Cover: safety cover or winter cover secured tight — a loose cover becomes a debris salad bowl

Step 3 — Winter monitoring (5 minutes a month)

• Check cover for standing water and pump it off — covers tear under load
• Peek at the water monthly: if it's cloudy but not green, you're winning
• After big storms, re-secure cover straps and check plug caps

Common closing mistakes

• Closing green. Killing an algae bloom under a cover in spring costs 10× the chemicals of fixing it now
• Skipping the chemical check in spring. Open with a full test set before swimming, not after
• Draining the pool "to be safe". An empty in-ground pool can pop out of the ground from groundwater pressure or crack its plaster. Never fully drain without professional advice
• Forgetting the chlorinator: trichlor left in a wet feeder over winter eats the feeder and stains the line

Warm-climate note (FL, AZ, SoCal)

If your water never freezes, you don't fully close — you reduce: cut pump run time to 4–6 hours, keep testing every 2 weeks, and maintain a low chlorine level. Freezing is the only reason to drain equipment.