When to close
Close once daily temperatures consistently stay below 65°F. In Delaware County that's usually mid-October through early November. Closing too early gives algae a chance to bloom under the cover; closing too late risks a freeze event.
What winterization actually does
Water in your plumbing lines expands 9% when it freezes — enough to crack PVC, breach fittings, and damage the pump housing. Winterization removes the water risk: lines get blown out with a high-CFM air compressor, antifreeze goes into the lines, and the pool water level drops below the skimmer.
Chemistry is boosted before close — shock plus algaecide plus stabilizer — so the water is protected all winter under the cover.
Cost of skipping it
A cracked pipe can turn a $500 winterization skip into a $3,000+ repair come spring. A frozen salt cell is $600–$1,200 to replace. A cracked skimmer housing means a plaster patch. Winterization is the cheapest insurance in the pool business.