In what order do I add closing chemicals?

Balance pH and alkalinity first, then add shock and run the pump for several hours, then add winter algaecide last. Adding algaecide at the same time as a heavy chlorine shock can burn it up before it does any good.

Should I shock before closing?

Yes. A closing shock knocks down anything living in the water so it does not bloom under the cover over winter. Use a double dose (about 2 lb of cal-hypo per 10,000 gal) and let it circulate before you add algaecide and cover.

Do these amounts fit every product?

No — they are typical rates to plan by. Concentrations differ between brands and between "closing kits" and individual bottles. Use the calculator to size the pool, then confirm against the label rate printed on the product you actually buy, and test your water with a kit.

Pool Winterizing Calculator

Scale the closing chemicals — winter algaecide, non-chlorine shock, chlorine shock, and stain & scale — to your pool's gallons, from typical label rates.

Inputs

Pool volume — gallons

gal

Amounts scale to your pool — no submit

Closing amounts for

15,000 gal

≈ 56,781 L

Winter algaecide (poly-quat 60%)4.5 fl oz (133 mL)

Non-chlorine shock (MPS)1.5 lb (680 g)

Winter chlorine shock (cal-hypo)3 lb (1.36 kg)

Stain & scale (sequestrant)48 fl oz (1.42 L)

Formula

amount = label rate per 10,000 gal × (your volume ÷ 10,000 gal)

These are typical closing rates — follow your product's label. Balance water first, then shock, then add winter algaecide last with the pump running.

Doses are estimates from published product concentrations — always follow the product label, add chemicals to water (never the reverse), test with a kit, and retest after dosing.

MeasureShedmeasureshed.com/calculator/winterizing-calculator

Pool winterizing — closing listUNITS: US GAL

Inputs

Pool volume15,000 gal

Results

Winter algaecide (poly-quat 60%)4.5 fl oz (133 mL)

Non-chlorine shock (MPS)1.5 lb (680 g)

Winter chlorine shock (cal-hypo)3 lb (1.36 kg)

Stain & scale (sequestrant)48 fl oz (1.42 L)

Closing order: balance pH & alkalinity → shock → run pump → add winter algaecide → lower water & blow out lines → cover. Follow each product's label rate.

Shopping list

☐ Winter algaecide (poly-quat 60%) — 4.5 fl oz (133 mL)

☐ Non-chlorine shock (MPS) — 1.5 lb (680 g)

☐ Winter chlorine shock (cal-hypo) — 3 lb (1.36 kg)

☐ Stain & scale (sequestrant) — 48 fl oz (1.42 L)

Formula

amount = label rate / 10,000 gal × (volume / 10,000 gal)

Doses are estimates from published product concentrations — always follow the product label, add chemicals to water (never the reverse), test with a kit, and retest after dosing.SHEET 1 OF 1

How it works

Closing a pool for winter is a short chemical checklist, and every item is dosed at a flat rate per volume — so much per `10,000 gal`. The calculator takes your pool's gallons and scales each closing chemical to match: winter algaecide, a shock, and a stain & scale sequestrant.

The typical label rates it starts from are a concentrated winter algaecide at about `3 fl oz` per `10,000 gal`, non-chlorine shock at about `1 lb` per `10,000 gal`, a closing chlorine shock at about `2 lb` per `10,000 gal`, and a stain & scale sequestrant at about `1 qt` per `10,000 gal`. Brands vary, so these are a planning baseline — **always follow the rate on your own product's label**.

Order matters as much as amount. Balance pH and alkalinity into range first, then shock and let the pump circulate for several hours, then add winter algaecide last so it is not immediately destroyed by the shock. Lower the water level, blow out the lines, and cover. Add every chemical to water with the pump running — never the reverse.

Worked example

Volume `15,000 gal`
winter algaecide = 3 fl oz × (15,000 ÷ 10,000) = `4.5 fl oz`
non-chlorine shock = 1 lb × 1.5 = `1.5 lb`
chlorine shock = 2 lb × 1.5 = `3 lb`

Questions about winterizing

A concentrated winter algaecide runs about 3 fl oz per 10,000 gal, so a 15,000 gal pool needs roughly 4.5 fl oz. Weaker algaecides call for much more — up to 12–16 fl oz per 10,000 gal — so read your label and match its rate.

SOURCES — Typical closing label rates: algaecide ~3 fl oz, non-chlorine shock ~1 lb, chlorine shock ~2 lb, sequestrant ~1 qt per 10,000 gal

Doses are estimates from published product concentrations — always follow the product label, add chemicals to water (never the reverse), test with a kit, and retest after dosing.