Liquid chlorine or cal-hypo — which should I use?

Liquid is easy to pour and leaves no residue but is weaker and short-lived. Cal-hypo is concentrated and cheap per pound but adds calcium hardness. Dichlor and trichlor add cyanuric acid. Pick by what your water already needs: if calcium and stabilizer are high, use liquid.

Why does the dose depend on my pool volume?

Because ppm is milligrams per liter — more water needs proportionally more product. A dose that is right for 10,000 gal will fall short in a 20,000 gal pool. Get your volume right first with the pool volume calculator, then dose.

Is it safe to guess and add extra "to be sure"?

No. Over-chlorinating wastes product, bleaches liners, and forces you to wait before swimming. Add the calculated amount, let the pump circulate, and **retest with a kit** before adding more. Follow the product label for handling and wait times.

Chlorine Dose Calculator

Enter your pool volume and current vs target free chlorine to get the exact amount of liquid chlorine, cal-hypo, dichlor, or trichlor to add — from each product's published strength.

Inputs

Pool volume — gallons

gal

Current FC

ppm

Target FC

ppm

Product — 12.5% available chlorine (sodium hypochlorite)

Results update as you type — no submit

Chlorine to add

26.3 fl oz

≈ 778 mL

FC change2 ppm

ProductLiquid chlorine 12.5%

Formula

raise FC by 2 ppm in 15,000 gal
chlorine = 26.3 fl oz ≈ 778 mL

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/chlorine-dose-calculator

Chlorine dose — dose sheetUNITS: US GAL · ppm

Inputs

Pool volume15,000 gal

Current FC1 ppm

Target FC3 ppm

ProductLiquid chlorine 12.5%

Results

chlorine to add26.3 fl oz

Other units778 mL

FC change2 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

☐ 26.3 fl oz (778 mL) — Liquid chlorine 12.5%

Formula

raise FC by 2 ppm in 15,000 gal

chlorine = 26.3 fl oz (778 mL)

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

Chlorine dosing is a mass balance. A "ppm" is one milligram per liter, so to raise free chlorine by a given amount you need `volume × ppm change × product strength` worth of product. The calculator works in liters internally, then converts to the fluid ounces, ounces, or pounds you actually measure out.

The only variable between products is the **available chlorine** percentage — the fraction of the product's weight that acts as chlorine. Liquid chlorine (sodium hypochlorite) is `12.5%`, cal-hypo is `65%` or `73%`, dichlor is `56%`, and trichlor is `90%`. A stronger product means less of it for the same result, which is why one gallon of `12.5%` liquid raises `10,000 gal` by about `15 ppm` while it takes roughly two pounds of `65%` cal-hypo to do the same.

Always add the product to a bucket of water or broadcast it across the deep end with the pump running — never pour water onto concentrated chemical. Test with a kit first, dose, then retest before adding any more. Dichlor and trichlor also raise cyanuric acid, so use them sparingly if your stabilizer is already high.

Worked example

Volume `15,000 gal` · free chlorine `1 → 3 ppm` (`+2 ppm`) · liquid `12.5%`
chlorine needed = 2 × 15,000 × 8.34 ÷ 1,000,000 = `0.25 lb` of available chlorine
liquid `12.5%` = 0.25 ÷ 0.125 ÷ 9.75 lb/gal = `26 fl oz` (`0.78 L`)

Questions about chlorine dosing

Per 10,000 gal, 1 ppm of free chlorine is about 0.083 lb (1.3 oz) of pure available chlorine. In product terms that is roughly 10.5 fl oz of 12.5% liquid, 2 oz of 65% cal-hypo, or 1.5 oz of 90% trichlor. Scale by your actual volume.

SOURCES — Product available-chlorine % (labels): liquid 12.5%, cal-hypo 65/73%, dichlor 56%, trichlor 90% · ppm = mg/L

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.