Pool Winterizing Calculator
| Gallons | Chlorine shock | Winterizer algaecide | Cover size for 16x32 |
|---|---|---|---|
| 10,000 | ~2 lb | ~1 qt | 16x32 pool → 20x36 cover (2 ft per side) |
| 15,000 | ~3 lb | ~1.5 qt | |
| 20,000 | ~4 lb | ~2 qt |
Pool closing is one chemical dose and one geometry problem: the kit scales with gallons - winterizer algaecide and chlorine shock measured per ten thousand gallons - while the cover scales with the pool's footprint plus the overhang that lets it float on the winter water table instead of diving into it.
Bottom line: close when the water holds below 65 degrees for a stretch of days, not by the calendar - closing warm is an invitation to algae, closing frozen is a cracked skimmer. Balance the water first (pH 7.2 to 7.6, alkalinity 80 to 120), shock, add the winterizer, drop the level below the returns, blow the lines, and the cover goes on last.
The honest part: the single biggest winterizing failure is not chemistry - it is water left in lines and equipment. Every cracked pump housing and split manifold in April traces to a line someone skipped blowing, which is why the plug-and-gizmo step outranks everything else on the list.
How to use
- Enter gallons (or let the pool volume calculator do the shape math) and read the chemical doses - shock, winterizer and oxidizer scale linearly.
- Read the cover size: footprint plus the overlap the manufacturer wants, usually two to three feet per side for above-ground, anchored for the wind.
- Work the checklist in order - balance, shock, lower, blow, plug, cover - and photograph the closed equipment pad; spring-you inherits the receipt.
Frequently asked questions
When should I close my pool for winter?
When the water temperature holds below 65 degrees - not the air temperature, the water, which lags weeks behind the weather. Closing while water is warm feeds algae a heated meal under a cover; closing after the first hard freeze risks skimmer and line damage during the work itself. Most temperate zones land the window between late September and early November.
What chemicals do I need to close a pool?
Three doses scaled to gallons: chlorine shock (about two pounds per ten thousand gallons), a winterizing algaecide (a quart per ten thousand), and optionally an enzyme or oxidizer to keep the cover scum down - plus balanced pH and alkalinity before anything else goes in. Stain-and-scale preventer earns its place in hard-water regions where spring staining starts in fall.
Should I drain my pool below the skimmer for winter?
Below the returns and skimmer mouth, yes - water left in the skimmer throat freezes and splits it - but never drain an inground pool substantially lower: hydrostatic pressure from groundwater can float or crack an empty shell. Above-ground pools drop to just below the return fitting; inground drops inches, then relies on plugs and antifreeze in the lines.
What size pool cover do I need?
The pool's footprint plus overlap - two to three feet per side on above-ground covers held by cable and winch, and a fitted safety cover ordered to the exact dimensions with anchor points for inground pools. A cover sized to the waterline collects the leaf soup directly in the pool; the overhang is what turns fall into a one-rake job on top instead of a spring vacuum below.