What a percentage makes comparable
The proportion of a product, by weight, that is chlorine available for disinfection. It is declared under chemical labelling rules rather than invented for marketing, and it is the figure that turns three incompatible chemistries into one comparable shelf.
It fixes something else that matters more than it first appears: it makes a price honest. Weight alone is not a basis for comparison on this shelf, because a kilogram of one compound does a different amount of work from a kilogram of another.
The three things it says nothing about
It does not promise a stabiliser load. Trichlor and dichlor are stabilised — they carry cyanuric acid, which protects chlorine from sunlight and which accumulates in the water because nothing removes it but dilution. Calcium hypochlorite carries none. The percentage says nothing about which of the two a product is, and the page prints the chemistry separately for exactly that reason.
It does not promise a pH behaviour. Trichlor is acidic, dichlor near-neutral, calcium hypochlorite alkaline. Each pulls the water a different way and each therefore sits alongside a different pH corrector.
And it does not promise anything about what your water needs. That is a matter of bathers, sunlight, rainfall and what is already dissolved, none of which is published by anyone.
The figures it is read beside
Chemistry, named in full — trichlor, dichlor, calcium hypochlorite — because it is what decides stabiliser and pH. Dose per cubic metre, which is the manufacturer’s own instruction. Dissolving speed or method, since a granule broadcast undissolved onto a vinyl floor bleaches it and a slow tablet is a different product in use from a fast one. And pack size, because opened chlorine absorbs moisture and cakes.
The whole disinfection shelf
The whole disinfection shelf: chlorine tablets, chlorine granules, bromine and active oxygen, each publishing an active content on the same principle. Winterising products too, where the relevant line is usually the absence of chlorine and the presence of something else, and where the published concentration is what makes two bottles comparable.
One safety line is repeated on every page in this group rather than stated once here: two chlorine products must never be mixed in the same bucket or dispenser, even in traces. That is the manufacturers’ own instruction and the safety data sheet’s, and this site reports it rather than qualifying it.
What readers keep writing in to ask
Does a higher percentage mean a better product?
It means more chlorine per kilogram, which makes the price per kilogram comparable. It does not mean the product suits the pool: trichlor is around 90 % and stabilised, so it also adds cyanuric acid with every tablet, and a pool already near its stabiliser ceiling is the case where the 65 % product is the right one.
Why compare on percentage rather than on price?
Because a five-kilogram tub at 56 % and a five-kilogram tub at 90 % are not the same purchase. Dividing price by available chlorine rather than by weight is what makes two shelves comparable, and it is the calculation the pages here set up by printing both figures.
Is the percentage the same as the dose?
No, and the two get confused constantly. The percentage describes the product; the dose per cubic metre is the maker’s instruction for using it. Both are published, both appear on the pages here, and neither is advice about a particular pool.
What about bromine and active oxygen?
They publish their own active content on the same principle — bromine as a percentage of available bromine, active oxygen as a percentage of the peroxide or persulphate compound. The figures are not interchangeable with chlorine, and the pages do not present them as though they were.
Last reviewed 21 September 2026