Winterize an in-ground pool in a freeze climate to prevent freeze damage to plumbing and equipment

Steps

1. Balance water chemistry (pH, alkalinity, calcium hardness, sanitizer/algaecide) before closing, since improperly balanced water sitting all winter under a cover promotes scaling, staining, or algae growth
2. Lower the water level appropriately for the skimmer/tile line and the specific closing method being used (mesh vs. solid cover), and blow out or otherwise clear water from skimmer lines, return lines, and other plumbing runs
3. Add pool-rated antifreeze (propylene glycol-based, non-toxic) to lines where residual water can't be fully evacuated, following manufacturer dosing guidance — never use automotive antifreeze
4. Install winterizing plugs/gizmos in skimmer and return lines, and remove/drain or otherwise protect equipment vulnerable to freeze cracking (pump, filter, heater, chlorinator) per manufacturer instructions
5. Install the appropriate cover (safety cover, mesh, or solid) rated for the pool and expected winter load (snow, debris) and secure it per manufacturer specs
6. Do a mid-winter check where practical (cover tension, water level, ice buildup) rather than assuming the closing will hold unattended all season