Salt Water level tested at 3600 ppm (twice) at pool test center. My Aqua Rite display shows 2800 ppm. After re-calibrating the Aqua Rite SWG control it reads approx. 3000 ppm, then starts to decrease at approx. 100 - 200 ppms per day until it reaches 2600 ppm at which time the "check salt" and...