Winterizing a pool: complete closing checklist

When to close

Close when daytime highs stay under 65 degrees for a week, usually late October in the Midwest and Northeast. Closing too early traps warmth and grows algae. Closing too late risks an unexpected freeze on full lines.

What you need

• Air compressor with a hose adapter ($25)
• Winter plugs for skimmers and returns ($1 each)
• Pool antifreeze (non-toxic, RV-safe)
• 2 to 4 gallons liquid chlorine
• 1 quart winter algaecide (Polyquat 60 or copper-free)
• Optional: winter pill (slow-release chlorine)
• Cover with water bags or anchors

Step-by-step

1. Balance and clean

A week before closing, balance: pH 7.4 to 7.6, alkalinity 80 to 120, calcium 200 to 400. Brush and vacuum so the pool starts winter clean.

2. Shock and add winter chemicals

Day before closing, shock to 10 ppm chlorine. Add winter algaecide per label dose.

3. Lower the water

Drain water 6 to 12 inches below the returns and skimmer mouths. In freeze country, below the lowest skimmer or you will crack tile and concrete.

For a vinyl liner, do NOT drain below the bottom of the skimmer or the liner can shift.

4. Blow out the plumbing

Hook the air compressor to the pump or to a dedicated blow-out port. Open one line at a time, blow until you see steady bubbles at the return or skimmer, then plug it. Repeat for every line.

5. Plug and antifreeze

Install rubber winter plugs (or Gizzmos in skimmers if you live where it freezes hard). Pour a cup of pool antifreeze in each line as a safety margin.

6. Drain equipment

Pump: open all drain plugs, remove the basket and lid. Filter: open drain. Heater: open drains and disconnect any water connections. Salt cell: remove and store inside.

7. Cover the pool

Pull a tight winter cover or safety cover. Water bags around the perimeter for a winter cover. Anchor straps for a safety cover. A loose cover lets in light and grows algae.

Common closing mistakes

• Not blowing lines completely (cracks pipes in spring)
• Leaving water in the pump or heater (cracks the casing)
• Using car antifreeze (toxic, will ruin the pool)
• Skipping winter algaecide (you open green)

When to call a pro

Hire a pro the first year if your equipment pad is complex (multiple heaters, automation, in-floor cleaning). Service charges $300 to $700 for a closing. After watching them once, most owners do it themselves the next year.