Above-Ground Pool Winterizing: The Wall Pressure and Chemistry Details

Closing an above-ground pool for winter isn't the same process as closing an inground pool, and most generic pool-closing guides gloss over the differences. The one that matters most is the ice expansion problem: ice in an above-ground pool pushes outward against the vinyl liner and the metal walls in ways that inground concrete or fiberglass construction can handle but above-ground construction often can't.

The air pillow and what it actually does

A pool air pillow inflated and placed at the center of the pool before the cover goes on serves as a controlled compression target. When ice forms on the surface and wants to expand outward, it pushes against the pillow rather than the pool walls. This significantly reduces the lateral wall pressure that can buckle an above-ground frame or crack a vinyl liner at the wall seam.

The pillow should be inflated to about sixty percent capacity — not fully inflated. A fully rigid pillow has no give and transfers pressure rather than absorbing it. Attach it loosely to the center of the pool with string so wind doesn't push it to one side before the cover traps it in place. Some pool owners use two or three smaller pillows spread across the surface on larger above-ground pools.

Water level and chemistry

Unlike inground pools, above-ground pools generally should not have the water level significantly lowered before closing. The water itself provides structural support that keeps the walls standing. Lowering it too much can allow the walls to bow inward. Follow your specific pool manufacturer's guidance — most recommend closing at normal operating level.

Check water chemistry a week before closing to allow time for corrections. pH between 7.2 and 7.6, alkalinity between 80 and 120 ppm. A balanced starting chemistry means the closing chemicals work correctly and you don't open to a stained liner in spring. A pool chemical testing kit handles the measurement. If the pool has a persistent algae problem, shock it a week before closing at double the normal dose to clear the water before adding closing algaecide.

Equipment removal and storage

Remove all deck equipment: ladders, rails, return jets (cap the wall openings after removal), skimmer basket. Store them out of the weather. Any deck equipment left installed through winter will have water trapped in it that freezes, and the expansion either damages the equipment or the fittings where it attaches to the pool wall.

Drain the pump, filter, and any connecting hoses completely. Blow air through the lines after draining — residual water in a garden hose-style connection will freeze and split the connection fitting. Store the pump and filter indoors. These are the most expensive components to replace, and they're the most vulnerable to freeze damage if stored outside.

What I'd skip

Skip leaving any winterizing chemicals — chlorine tablets, bromine — in the skimmer or any in-line feeder through the winter. Concentrated chemicals sitting against plastic fittings over six months bleach, embrittle, and eventually crack the components they're sitting in. Add them to the water properly during the closing process, then remove all feeders. Also skip the impulse to partially drain an above-ground pool for any reason other than what your manual specifies. The water is part of the structural equation for these pools in ways that aren't obvious, and a misguided drain-down is a common source of above-ground pool collapses.