Since your cell is generating chlorine, you might try cleaning the sensors with rubbing alcohol. I had a similar problem last year with my Aquapure. It wasn’t reading zero, but was reading so low that it was producing a fault error with my cell. I knew from testing that the salt level was a little over 3,000. I thought for sure my cell was failing, as those were the symptoms that had shown up prior to a previous failure, but I tried cleaning the sensors and, go figure, it worked! After a quick rubdown with the alcohol, the cell was reading correctly and has been ever since. There wasn’t any visible residue, but there must have been something on them.