A cell wears out and that is normal
Plates have a service life measured in thousands of hours. A cell at the end of its life reads correctly and produces badly. We check the hours and inspect the plates rather than adding salt to a cell that cannot use it.
Scale is the other half
Calcium builds on the plates and insulates them. It comes off in an acid bath — a service, not a part. A company that sells you a cell without first inspecting the plates has not looked.
Salt is not the same as chlorine
Adding salt raises salinity, not sanitizer. If the pool is low on chlorine the answer is the cell's output, the run time, or the stabilizer holding it back.
Tell us about the pool. We will tell you the next opening.
The chat takes the symptom and the address, then hands it to the desk. It books visits — it never tries to diagnose a pool in a chat window.