I have an Aquapure 1400. About 3 weeks ago, I started to get a low salt indication, making the cell turn off. I cleaned the cell; sensor and pool filter, and then was getting correct salt readings 3.1-3.2, cell on and functioning properly. After about a few hours, the reading starts dropping to 2.8, 2.6, Etc. until it gets low enough to turn the cell off. This takes about 1-2 days. I then can remove the sensor, clean it with a green scrub brush, re-install it, and then it will read 3.1-3.2 again. I'm not sure what to do. It seems to me if the sensor is bad, cleaning it would not make it start working. Any suggestions?