What the chemistry actually does
Nothing is fixed by a body here — this is chemistry rather than convention. What is fixed is behaviour: cyanuric acid binds chlorine loosely, shields it from ultraviolet, and releases it as free chlorine is consumed. A stabilised pool in July loses a fraction of the chlorine an unstabilised one does.
The second fixed behaviour is the one that catches people out. The compound is stable. It stays.
Why more stabiliser is not more disinfection
It does not promise more disinfection. Stabiliser slows chlorine’s destruction by sunlight; it does not add any. A pool with a high stabiliser reading and a low free chlorine reading has plenty of protection and nothing to protect.
It does not promise a threshold. Recommended maxima are published by manufacturers and by national rules, they differ, and this site names neither as the figure — it reports what a given maker states for a given product.
And it does not promise that a higher reading is a fault. A pool topped up regularly with fresh water behaves differently from one that never overflows, and the same dosing routine produces different readings in the two.
The readings that only make sense together
Free chlorine, which is the figure stabiliser exists to preserve and which a test strip reads separately. The chemistry of whatever is being dosed, since that decides whether the reading climbs at all. Total alkalinity and pH, which move with the chemistry too — trichlor pulls pH down, calcium hypochlorite pushes it up. And the parameters a test strip or photometer actually reads, because a figure nobody measures is a figure nobody manages.
Where the reading decides the purchase
Chlorine tablets and granules, where the chemistry line on every page says whether a product is stabilised. Test strips and water testers, where the parameter list decides whether the reading is available at all. And winterising products, several of which are chosen precisely because they do not add to it over a closed season.
What readers keep writing in to ask
Which products contain stabiliser?
Trichlor tablets and dichlor granules are the two stabilised chlorines, and both carry cyanuric acid as part of the molecule rather than as an additive. Calcium hypochlorite carries none, and neither do bromine or active oxygen. Pages here name the chemistry for every product on the shelf for this reason.
Why does stabiliser accumulate?
Because nothing in a pool removes it. It is not consumed by disinfection, it does not evaporate, and a sand or cartridge filter passes it straight through. What lowers a reading is fresh water — backwashing, splash-out, rain overflow — and nothing else.
Is there a maximum?
Manufacturers and national rules state figures, and they differ between countries and between makers. This site reports the figure a given manufacturer publishes for their own product and points at the local rules rather than naming a threshold of its own, because that threshold is not ours to set.
Do test strips measure it?
Many do, and the pages here list the parameters each strip covers. A strip that reads free chlorine, pH and total alkalinity but not cyanuric acid cannot tell you anything about the figure this page is about, which is worth knowing before buying one.
Last reviewed 21 September 2026