Why chlorine and CYA must be read together.
The same free chlorine number can mean different sanitizer availability depending on stabilizer levels.
← Back to Water ChemistryWhat does cyanuric acid do?
Cyanuric acid (CYA) helps outdoor chlorine resist sunlight loss. It also holds much of the chlorine in a stabilized form, reducing the immediately active sanitizer fraction. More CYA therefore generally requires more free chlorine to maintain comparable chlorine activity.
Why a single chlorine number isn't enough
Pool owners sometimes compare two pools based only on free chlorine ppm. But a pool with 40 ppm CYA and one with 90 ppm CYA do not have equivalent sanitizer conditions at the same chlorine reading.
Our working targets
Pure Pools often targets 35–50 ppm CYA for outdoor pools and adjusts free chlorine according to CYA, usage and sanitizer demand. Our typical chlorine working range is 2–7 ppm, but some circumstances or codes require different limits. A simple FC/CYA percentage does not establish that water is safe to swim in.
Why this affects chemical choices
Trichlor tablets and dichlor add CYA as they chlorinate; liquid chlorine does not add stabilizer. Ongoing treatment choices influence future water chemistry and should be made with current testing data.
We rely on accurate testing and applicable public-pool rules rather than a single chlorine-to-CYA ratio for every pool.
Continue learning about water chemistry.
Explore more of the science behind Pure Pools' approach or review your pool's readings in our calculator.