How much liquid chlorine per 10,000 gallons?

About 10.7 fl oz of 12.5% liquid chlorine raises free chlorine by 1 ppm per 10,000 gallons. To raise FC by 3 ppm you would add roughly 32 fl oz (about a quart).

How much cal-hypo to add?

Compute available chlorine (gallons × Δppm × 8.34 × 10⁻⁶) and divide by the product strength. For +10 ppm in 10,000 gallons with 73% cal-hypo: 0.834 ÷ 0.73 ≈ 1.14 lb.

Why do chlorine products have such different doses?

Because they contain different fractions of available chlorine — liquid ~12.5%, dichlor ~56%, cal-hypo ~73%. The same FC increase needs far fewer pounds of a stronger product.

When is the best time to add chlorine?

In the evening, with the pump running. Sunlight breaks down unstabilized chlorine quickly, so dosing after sunset lets it circulate and work overnight. Re-test the next day.

How much chlorine to add to a pool (liquid, cal-hypo, dichlor)

Different chlorine products have very different strengths. Here is how to dose any of them to hit a target free-chlorine level.

By Francesco Zinghinì

Safety: dosing figures are estimates. Follow the product label, add one chemical at a time, never mix pool chemicals, add chemical to water (never water to chemical), keep chemicals away from children, and re-test before swimming. Add about ¾ of a dose, re-test, then top up. Not a substitute for professional pool service.

Chlorine dosing has two parts: how much available chlorine you need to raise free chlorine (FC) by the gap you want, and how much product that is once you account for the product’s strength. Liquid chlorine, cal-hypo and dichlor all deliver chlorine, but at very different concentrations, so the pounds or ounces differ a lot.

The two-step formula

First, the available chlorine to raise FC by Δppm, using the same 8.34 lb/gal solute rule as salt:

available chlorine (lb) = gallons × Δppm × 8.34 × 10⁻⁶

Then convert to product by dividing by its strength fraction:

product (lb) = available chlorine ÷ strength

Typical strengths are liquid chlorine 12.5% (0.125), cal-hypo 73% (0.73) and dichlor 56% (0.56). For liquid chlorine there is a handy shortcut in fluid ounces:

fl oz of 12.5% liquid = (gallons ÷ 10,000) × Δppm × 10.7

Worked examples

Raise a 10,000-gallon pool by 3 ppm with 12.5% liquid chlorine: (10,000 ÷ 10,000) × 3 × 10.7 = 32.1 fl oz — about a quart.

Raise a 10,000-gallon pool by 10 ppm with 73% cal-hypo: the available chlorine is 10,000 × 10 × 8.34 × 10⁻⁶ = 0.834 lb, and dividing by 0.73 gives ≈ 1.14 lb of cal-hypo.

The pattern to remember: about 10.7 fl oz of 12.5% liquid per 10,000 gallons raises FC by 1 ppm. Everything else scales from there.

Choosing a chlorine product

Liquid chlorine (sodium hypochlorite, ~12.5%): no cyanuric acid or calcium added, raises pH slightly, ideal for regular dosing and shocking. Loses strength on the shelf.
Cal-hypo (calcium hypochlorite, ~65–73%): strong and stable in storage, but adds calcium hardness over time — worth watching in hard-water areas.
Dichlor (~56%): convenient and fast-dissolving, but adds cyanuric acid with every dose, which can over-stabilize a pool if used continuously.

Because dichlor and trichlor add CYA and cal-hypo adds calcium, the “which product” question is really about what else you are adding to the water, not just the chlorine.

Dosing tips

Enter the product’s actual strength from the label — brands vary, and liquid chlorine weakens as it ages. Dose with the pump running, ideally in the evening so sunlight does not burn off the chlorine before it works, and re-test after a circulation cycle. Keep free chlorine appropriate to your cyanuric acid level; a stabilized pool needs a higher FC to stay effective. Never mix chlorine products or pour different chemicals together.

Matching chlorine to your CYA level

How much free chlorine you need to keep is not a fixed number — it rises with your cyanuric acid (stabilizer) level. CYA protects chlorine from sunlight, but it also holds some chlorine in reserve, so a pool at 50 ppm CYA needs a higher free-chlorine target than one at 30 ppm to stay equally sanitary. Test both and keep free chlorine proportional to CYA rather than aiming at a single universal number. If you sanitize with dichlor or trichlor, remember every dose also raises CYA, which over a season quietly pushes your required chlorine higher.

Daily demand and keeping a residual

A pool consumes chlorine constantly — sunlight, swimmers, sweat, sunscreen and organic debris all burn it up. The goal is to replace that daily demand and always keep a residual, so free chlorine never hits zero. Sun-exposed, heavily used pools may need chlorine every day or two; a shaded, lightly used pool needs less. Dose in the evening so sunlight does not destroy it before it works, run the pump to circulate, and test regularly to learn your pool’s rhythm. Bear in mind that liquid chlorine weakens on the shelf, so an older jug delivers less than its label — buy it fresh and in quantities you will use within a few weeks. A salt generator automates all of this by making chlorine on the fly, but you still set its output to match demand and top up by hand during peaks.

The bottom line

Chlorine dosing is two quick steps: find the available chlorine to raise free chlorine by the gap you want, then divide by your product’s strength to get the actual pounds or ounces. The anchor to remember is about 10.7 fluid ounces of 12.5% liquid per 10,000 gallons for each 1 ppm of free chlorine — everything else scales from there. Choose the product for what else it adds: liquid stays neutral, cal-hypo adds calcium, and dichlor adds cyanuric acid. Enter the real, current strength from the label, dose in the evening with the pump running, and keep your free chlorine matched to your CYA level rather than to a single universal target. Test often, never mix products, and always add chemical to water — and you will hold a clean, sanitary pool with minimal fuss.

Get exact amounts for your product and readings on the chlorine calculator, size a bigger correction with the shock calculator, and check your stabilizer with the cyanuric acid tool.