Most pool closing guides tell you to balance the water, drop the level, and pull the cover over. Almost none of them tell you what to do with a FROG system — which matters, because leaving one in a closed pool all winter is how people destroy a perfectly good holder and come back in spring to a corroded mess.
First: should you close at all?
This depends entirely on where you live, and a lot of advice online quietly assumes you're in Ohio.
If your water freezes — the Midwest, Northeast, mountain states — yes, close properly. Freezing water expands, and expanding ice is what cracks plumbing and splits above-ground walls.
If you're in Florida, the Gulf Coast, south Texas, Arizona or coastal California, you generally don't close at all. You reduce. Run the pump fewer hours, keep sanitizer going at a lower level, and keep skimming — because leaves still fall here, and a pool left unattended for four warm months turns green far faster than one under ice. Skip to the warm-climate section below.
Take the FROG system out before you close
This is the step that gets missed. Whatever system you're running — Flippin' FROG, Flippin' FROG XL, or an in-line Pool Frog 5400 or 6100 — the cartridges and holder should not spend the winter sitting in still, cold, covered water.
Chlorine cartridges and Bac Pacs: don't overwinter them. Chlorine cartridges are consumables designed to deplete in weeks, and one sitting in stagnant water for months does nothing useful while slowly degrading the holder around it. Use it up before closing or discard it.
Mineral cartridges: these are the ones worth saving. A mineral cartridge runs up to six months. If yours went in recently and has real life left, rinse it in fresh water, let it dry completely, and store it indoors somewhere above freezing. Write the install date on it with a marker — by April you will not remember.
If the cartridge is near the end of its six months, don't try to stretch it across the winter. Start spring with a fresh one.
The holder itself: rinse in fresh water, dry fully, store inside. Don't leave it in the skimmer.
For in-line Pool Frog 5400 and 6100 systems, the reservoir sits in your plumbing at the equipment pad. When you blow out the lines, pull the reservoir, empty it, dry it and store it with everything else. Water left in the housing is the same freeze risk as water left in a pipe.
Then close the water properly
Balance before you cover, not after. Once the cover is on you're not adjusting anything until spring, so whatever the water is on closing day is roughly what it stays.
- pH 7.2–7.6 and alkalinity 80–120 ppm. Water that sits acidic all winter etches surfaces and corrodes metal.
- Calcium hardness in range — too low pulls calcium out of plaster and grout.
- Shock, then wait. Let chlorine fall back to normal before covering. Covering over high chlorine can bleach the underside of the cover.
- Clean first. Brush the walls, vacuum the floor, empty the skimmer. Anything organic you leave behind spends the winter feeding algae.
The cover, and why the air pillow matters
On an above-ground pool, the air pillow is not optional padding. It sits under the cover and absorbs the pressure when the surface freezes, so ice pushes inward against the pillow rather than outward against a flexible wall. Skipping it is one of the more common ways above-ground pools get damaged over winter.
A leaf net stretched over the winter cover is the other piece worth having. It catches debris before it settles onto the cover, so spring opening is lifting off a loaded net rather than dredging sludge.
Warm climates: what to do instead
Keep the FROG system running. Bather load drops to nearly nothing over winter, which means your sanitizer demand drops too — but it doesn't go to zero, and neither does algae, which stays active well into the 60s.
Cut pump runtime, keep testing every week or two, and keep skimming. A mineral system is genuinely well-suited to this stretch, because it holds a low, steady sanitizer level with very little intervention — which is exactly what an unused pool needs.
Spring
Open with a fresh chlorine cartridge, always. Check the date you wrote on the mineral cartridge and replace it if it's past six months of active use. Rinse the holder, reinstall, and test before anyone gets in.
Browse FROG cartridges and refills, or see everything for above-ground pool closing.
