Winterizing an in-ground pool well is the difference between “open in April, swim in May” and “spend three weekends fixing what froze in February.” This is the complete step-by-step winterization checklist for an in-ground pool in a cold climate.
When to winterize
Aim for sustained water temperatures below 65°F. Closing too early (warm water + cover = algae bloom). Closing too late (one hard freeze before you’re ready = cracked equipment). For most of the Midwest and Northeast, this is mid- to late October. The Sun Belt may never need full winterization — just a partial close.
Step-by-step winterization
Target: pH 7.4–7.6, alkalinity 80–120 ppm, calcium hardness 200–400 ppm. Test the day before closing and adjust. Closing with bad chemistry means stains, scale, or etching over winter.
Anything you leave on the floor will become a stain by spring. Use the wall brush on all surfaces, then vacuum to filter (not waste).
Run the pump for 8 hours after shocking so the chlorine fully circulates.
A polyquat-based winter algaecide prevents bloom during 5+ months under the cover.
For mesh safety covers: 4–6 inches below the skimmer mouth. For solid covers: just below the skimmer. Use a submersible pump or backwash to waste until you hit the right level. Never close with water in the skimmer line.
Use a shop vac or air compressor to push water out of every suction and return line. Continue until you see bubbles coming from the pool side of each line. Then plug each line with a rubber freeze plug.
Remove every drain plug from the pump body, filter housing, and heater. Drain the pump strainer pot. Remove the pressure gauge (leaving it in often cracks). Remove the strainer basket and lid o-ring; store in the basement.
If you have a salt chlorine generator, disconnect the cell from the plumbing and bring it inside. Leaving the cell outdoors all winter destroys the titanium plates.
Mesh safety cover: spring-strap into anchor brass at each anchor point. Solid cover: spread evenly and anchor with water bags. Walk the cover perimeter and verify no gaps.
Place an automatic cover pump (with non-freeze hose) on top of the cover to remove rain and snow melt before they overload the cover.
Closing chemistry pack
Durachlor Closing Shock
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CoverBlast Non-Freeze Hose
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Durachlor Chlorine Stabilizer
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