If you are in the dry, hot part of Texas, with kinda bad water even when it's not dry . . . yeah, you could see your 'salt' increasing as you replace evaporated water.

The reason is, SWCG's measure conductivity (how easily electricity passes through the water) not salt. This usually works OK, because conductivity increases when salt increases. The problem for you is ANY kind of salt (say, sodium sulfate) increases conductivity, but only chloride salts increase SWCG capacity.

It would probably be worthwhile to ask your water company for a copy of their most recent annual water analysis, and post the results here. (You don't need to include trace pesticides and radionuclides, etc., just ordinary anions & cations.)

Build up of certain salts can cause problems.