How much chlorine to add to raise a pool’s level, corrected for the strength of whatever product you have.
Currency and number format for
Product to add
—
Product to add—
If it is liquid—
Pure chlorine equivalent—
Rise needed—
Volume—
For a shock treatment—
How this was worked out
Indicative result. This is the arithmetic of dilution with whatever product you declare. Suitable levels, compatibility between products and safe handling depend on the type of pool and on the manufacturer: never mix different products, and always follow the instructions on the container.
The formula
grams of pure chlorine = rise in ppm × cubic metres
Where it comes from
The basis is a clean equivalence: one part per million is one gram per thousand litres, so raising one ppm in a cubic metre of water takes exactly one gram of pure chlorine. Everything else is correcting for the real product, which is never pure chlorine: solid calcium hypochlorite runs around 70 % and liquid sodium hypochlorite far less. Hence strength being a field: for the same target, very different amounts are needed depending on what is in the container.
How to work it out by hand
Convert the pool volume to cubic metres
Subtract the chlorine already there from the level you want
Multiply by the cubic metres: those are the grams of pure chlorine
Divide by the strength of the product as a decimal
What is worth knowing
Free chlorine is not the only thing that counts. If the pH is high, chlorine loses effectiveness dramatically: at pH 8 it disinfects around a quarter as well as at pH 7.2, so adding more chlorine without correcting the pH is throwing product away. Stabiliser — cyanuric acid — protects chlorine from sunlight, but above a certain level it locks it up, and then the test shows chlorine that does not disinfect. And a warning that is not theoretical: never mix different products, and never add water to chlorine; the product always goes dissolved and added to the water, not the other way round.
Frequently asked questions
How much chlorine should I add to my pool?
One gram of pure chlorine per cubic metre for every ppm you want to raise. With a 70 % product, that is 1.43 grams.
How much chlorine for 50,000 litres?
To go from 0.5 to 1.5 ppm with a 70 % product, about 71 grams. For a shock treatment, over a kilo.
What free chlorine level should a pool have?
Usually between 1 and 2 ppm in a pool in use. The exact level depends on the type of pool and the product, and is on the label.
Why is the chlorine not working?
Almost always the pH. At pH 8 chlorine disinfects a quarter as well as at 7.2, so correct the pH before adding more.
What is shock chlorination?
Raising chlorine to about ten times the normal level to break down chloramines when the water is cloudy or smells strongly.
Can chlorine products be mixed?
No. Different products can react dangerously with each other. Each is dissolved separately and added to the water, never water onto the product.
Cookies
We use our own cookies to remember your preferences: country, number format and the calculators you use most. Analytics and advertising cookies are only switched on if you accept them. More information.