Winterizing
Also called: winterization, closing for winter, winter mode.
Winterizing is getting a pool through winter, and it is two entirely different jobs depending on where you live. In freeze country it means a hard-freeze close: drain the plumbing so it doesn't split and seal the pool under a cover. In Florida you don't close; you switch to winter mode.
Why it matters
Pick your track first. Florida winter mode: chlorine demand drops with the sun angle, the salt cell stops generating in cold water so you switch to liquid chlorine, you cut pump run time to whatever keeps the water mixed, and you keep pH up so a plaster surface doesn't etch. On the two or three freeze nights a year, run the pump all night, and don't rely on a variable-speed pump's freeze mode. On an above-ground pool the wall decides: a rigid steel or resin wall stays up and is winterised, while Intex says an Easy Set or frame pool comes down below 41°F.
In numbers
Pentair's IntelliChlor turns off at 52°F, ±3°F, and Hayward's Aqua Rite automatically stops generating below 50°F. Both are documented in the manuals, so a quiet cell in a Florida cold snap is not a broken cell.