How to winterize an above ground pool

When to close an above ground pool

Close when the water has fallen to about 65°F (18°C) and is still dropping. Below that, algae growth slows sharply and chlorine demand collapses, so the water holds its condition with far less help. Close while it is still warm and you are sealing up a pool that is actively growing things.

The trade-off is leaves. A late close means more debris has already sunk and less time to deal with it. If your property has heavy leaf fall, plan a mid-autumn close and accept one or two extra cleanings rather than closing early.

Step 1: clean it while you still can

Whatever you leave in the pool stays there all winter — under a cover, in the dark, with no circulation. Vacuum the floor, brush the walls and steps, empty both baskets and skim the surface.

Run your hand along a wall. A slippery film means algae has already started. That is a brush and an extra filter run now, or a green pool in April.

If the water is already hazy, work through our cloudy water diagnostic order before you close. It is much easier to fix while the pump is still running.

Step 2: balance the water before anything else goes in

Get pH, total alkalinity, calcium hardness and sanitizer into range before you close, and write the numbers down somewhere you will actually find them in spring.

An unbalanced pool then sits for months with no circulation to correct it. High pH with high calcium is how you get scale that has to be scrubbed off in spring. Low pH with low alkalinity is how you get a corroded ladder and a stained liner.

Step 3: lower the water level

Above ground pools are held in shape by the water inside them. That single fact drives this step.

• Lower the water to just below the skimmer and the return fitting — commonly about 4–6 inches below the skimmer — so ice has somewhere to expand.
• Or keep the level up and fit a skimmer freeze guard: a compressible plug that sits inside the skimmer body and absorbs the expansion for you.
• Do not go any further than that.

Step 4: protect the skimmer and the return

• Remove the skimmer basket, the weir flap and any hose.
• Fit a freeze guard, or plug the skimmer throat with a purpose-made winter plug.
• Plug the return fitting from inside the pool.
• If your pool uses over-the-wall hoses instead of through-wall fittings, just remove them all — there is nothing left to freeze.

The rule is simple: anything holding water inside a rigid plastic body is a cracked fitting waiting for the first hard freeze.

Step 5: winter chemicals — follow the label, not us

A winterizing kit usually pairs an algaecide with an oxidiser designed to be dosed once and left alone. That is the right shape for winter: you want something that keeps working when nothing is circulating.

We do not publish our own dose numbers here. The amount depends on your water volume and on the concentration of the product you actually bought, and the product label is the authority on both. Work out your pool volume first, then follow the label.

Step 6: drain and store the equipment

• Pump: drain the housing completely.
• Filter: drain it. If it is a sand filter, an end-of-season deep clean is worth the effort.
• Heater or heat pump: drain it, and store it indoors where the manufacturer says to.
• Hoses, skimmer basket, ladder, pressure gauge and test kit: indoors.

A cupful of trapped water is enough to split a housing over a hard freeze. Drain everything, then leave the drain plugs out.

Step 7: cover it so water cannot pool

• Use an air pillow. It floats in the middle, gives expanding ice somewhere to go, and stops the cover being dragged down into the water.
• A solid cover needs a cover pump. Rain and meltwater collecting on top are dead weight pulling on the top rail and the wall.
• A mesh cover drains itself and needs less attention — but it lets light through, which is why some mesh-covered pools go green by spring.
• Tie the cover down evenly. Uneven tension is how top rails bend.

Leave a little slack. A cover pulled drum-tight in October has nowhere to go when the ice expands in January.

Step 8: check it through the winter

• Pump standing water off a solid cover rather than letting it freeze into a solid block.
• After heavy snow, do not chip ice off with a shovel or an axe — you will puncture the cover.
• Keep children and pets off the cover.

The six mistakes that cost people a liner

1. Closing in warm weather, which seals an active algae problem in for the winter.
2. Draining the pool, which risks the liner and the walls.
3. Skipping the air pillow, then wondering why the cover sank.
4. Leaving hoses connected, then finding them split in spring.
5. Balancing the water after closing instead of before.
6. Forgetting the skimmer — the single most commonly freeze-cracked part on the whole pool.

Questions people ask before their first close