Chlorine lock (stabilizer lock)
A popular but misleading term for what happens when cyanuric acid (stabilizer) builds up so high that chlorine becomes too weak to sanitize effectively.
'Chlorine lock' describes a pool where chlorine reads on a test strip but doesn't seem to be doing its job, usually because cyanuric acid (the stabilizer that protects chlorine from sunlight) has crept up to 80-100+ ppm over repeated doses of stabilized chlorine products. At that concentration, CYA doesn't literally 'lock' chlorine in a chemical sense, but it does bind chlorine so tightly that its sanitizing strength drops dramatically even at a normal-looking free chlorine reading. The fix is diluting the water (partial drain-and-refill) to bring CYA back into the 30-50 ppm range, or switching to an unstabilized chlorine source until it does.
Track this with Skimmer — log water tests and keep every reading in one place.
See pricing →