Hard-freeze close
Also called: closing a pool, pool closing, winter close.
A hard-freeze close is the full winter shutdown for a pool whose water reliably drops below 60°F for weeks and whose air goes below freezing for sustained stretches: balance the water, lower it, clear or remove the plumbing, and cover the pool. Warm-climate pools do not close; they run in winter mode.
Why it matters
Wait until the water is solidly below 60°F; closing early is the number-one cause of a green opening. Balance to pH 7.6-7.8, SLAM two or three days ahead, let FC drift to 20% of CYA, and add a max dose of PolyQuat. In-ground, the cover manual sets the water level. Blow the lines with a low-pressure blower (Pentair and Hayward both say under 5 PSI), pull the drain plugs, and use propylene-glycol antifreeze, never automotive. On a rigid-wall above-ground pool, get the water out of the skimmer without dropping past your cover's stated maximum, and bring the pump and hoses indoors. Intex says a soft-side pool comes down below 41°F.
In numbers
You only need about 3.5 psi to clear a pipe 8 feet below water level, and typical 2" pool plumbing has a bursting pressure around 890 psi. So the goal when blowing lines is volume, not pressure.