What are your water temperatures like during the day and overnight, especially when the cell is running?
If your salt level is on the low end and the water temp drops, SWGs that are not temperature compensated will show a salt level that drops with temperature. It's not actually the salt that is changing, it's the conductivity of the water that is changing. Warmer water conducts electricity better than colder water and the SWG will register that as a drop in salinity.
Do you have a salt test kit (K-1766)? You need to check your salt level and see if adding salt to make the SWG happy is possible. If your true salt level is normal or high and the cell is saying its low, then the cell either needs to be cleaned or it is dying.
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