Pool Shock Dose Calculator to Clear Chloramines

Get the breakpoint shock dose that drives free chlorine to about 10x your combined-chlorine reading, clearing chloramines — retest FC and CC afterward.

Inputs
gal
ppm
ppm
Results update as you type — no submit
ResultsLIVE
Shock to add
12.3 oz
≈ 349 g
Breakpoint target (10× CC)6 ppm FC
FC change4 ppm
ProductCal-hypo 65%
Formula
raise FC by 4 ppm in 15,000 gal
shock = 12.3 oz ≈ 349 g
Add chemicals to water, never water to chemicals. Broadcast over the deep end with the pump running, then retest before adding more.
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/pool-shock-calculator
Pool shock — dose sheetUNITS: US GAL · ppm
Inputs
Pool volume15,000 gal
Current FC2 ppm
Combined chlorine0.6 ppm → target 6 ppm
ProductCal-hypo 65%
Results
shock to add12.3 oz
Other units349 g
FC change4 FC ppm
Safe dosing: add product to water (never the reverse) · broadcast with the pump running · wait and retest before re-dosing · keep chemicals apart and dry.
Shopping list
☐ 12.3 oz (349 g) — Cal-hypo 65%
Formula
raise FC by 4 ppm in 15,000 gal
shock = 12.3 oz (349 g)
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

Shocking a pool means raising free chlorine high enough to break apart combined chlorine — the chloramines that make eyes sting and give a pool that "chlorine smell." The published target is **breakpoint chlorination**: drive free chlorine to about 10× your combined-chlorine reading. If combined chlorine tests at 0.6 ppm, the breakpoint target is 6 ppm of free chlorine.

The calculator takes your current free chlorine and combined-chlorine readings, computes the breakpoint target, and then works out how much product it takes to make up the difference across your pool's volume — using each product's published available-chlorine strength. Cal-hypo at 65% and dichlor at 56% are common shock products; liquid chlorine works too and adds no calcium or stabilizer.

Shock late in the day so sunlight does not burn off the chlorine before it finishes the job, run the pump for several hours, and **retest before swimming** — most labels want free chlorine back under 4 ppm first. Add product to water, never the reverse, and keep it clear of your skin and eyes.

Worked example
Volume 15,000 gal · current FC 2 ppm · combined chlorine 0.6 ppm
breakpoint target = 10 × 0.6 = 6 ppm → need +4 ppm
cal-hypo 65% = 4 × 15,000 × 8.34 ÷ 1,000,000 ÷ 0.65 = 0.77 lb = 12 oz

Questions about shocking a pool

Enough to reach 10× your combined-chlorine reading. For a 15,000 gal pool that needs to go from 2 to 6 ppm free chlorine, that is about 12 oz of 65% cal-hypo or roughly a half-gallon of 12.5% liquid chlorine. Read combined chlorine on your test kit as total minus free.

SOURCES — APSP-11 / CDC MAHC breakpoint chlorination (10× combined chlorine) · product available-chlorine %
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.

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