A well-executed pool closing sets up an easy spring opening. A rushed or incomplete closing sets up a green pool, freeze-cracked plumbing, and damaged equipment — all of which cost far more to fix than they would have to prevent. This is the complete protocol.
The ideal closing window is when water temperature drops consistently below 60°F. Above 60°F, algae and bacteria remain active even under a cover. Closing too early in warm weather means a longer period of stagnant, undertreated water. Closing too late risks freezing plumbing before you finish.
In climate-variable regions: watch the 10-day forecast, not just the current temperature. You want the closing completed at least 2 weeks before the first expected hard freeze.
The water that goes under the cover needs to be balanced enough to remain stable all winter. Test and adjust:
| Parameter | Closing Target | Why |
|---|---|---|
| pH | 7.4–7.6 | Prevents staining and equipment corrosion |
| Total Alkalinity | 80–120 ppm | Stabilizes pH over winter |
| Calcium Hardness | 175–225 ppm | Prevents plaster etching from soft water |
| Free Chlorine | 3–5 ppm at closing | Starting point for winter treatment |
| CYA | 30–50 ppm | Protects chlorine from UV until cover fully on |
After balancing, shock the pool with 2 lbs of calcium hypochlorite per 10,000 gallons (or equivalent liquid chlorine). Run the pump for 8 hours after shocking before closing equipment.
Add a winter algaecide (polyquat 60 type — not the standard 10% formulation). Winter algaecides are formulated to remain effective at low temperatures and over extended periods. Add clarifier to maximize water clarity before covering.
Water level depends on your winter cover type:
This step is critical in regions that freeze. Water left in skimmer lines, return lines, or heater plumbing will expand when it freezes, cracking PVC pipes, split fittings, and damaging heater manifolds. A single freeze-cracked line costs $200–600 to repair in spring.
Document every closing in PoolLens: water chemistry at closing, which lines were blown, where drain plugs are stored, and any items needing follow-up in spring. This information is worth its weight in gold when you return in March with a fresh crew.
Store closing chemistry, line blow-out completion, cover type, and open items per account. When spring opening season hits, every account is ready to open efficiently — not re-diagnosed from scratch.
Open PoolLens Free →No — never fully drain an inground pool for winter. The hydrostatic pressure of groundwater can lift or crack an empty pool. Drain only enough water to get below the return jets and skimmer if your method requires it.
Close when water temperatures consistently drop below 60°F. Algae cannot grow effectively below 60°F, so closing too early in warm weather creates a long period of potentially undertreated water under a cover.
A standard wet/dry shop vac set to blow mode works for most residential plumbing configurations. Blow each line from the equipment pad until air rather than water exits at the pool end, then plug immediately.
Closing chemicals: shock (calcium hypochlorite or liquid chlorine), winter-grade algaecide (polyquat 60 type), a sequestering agent if metals are present, and stain prevention treatment for plaster pools.