If you truly want to track salt concentration as a proxy for leak detection, then your testing needs to be more calibrated (i.e., use a larger water sample to gain a deeper titrant precision) and you need to ignore the IC salinity output. The Pentair ICs are probably the worst of the breed when it comes to measuring salinity and I all but ignore the readout value and simply look for the system to say that the salt cell is OK.
Track your salinity every few days with the K-1766 and turn off your autofill. Add fill water manually and use a hose-end water meter to get precise input volumes. You'll also want to measure the salinity of your fill water as all municipal supplies have some residual chloride level (mine fill water has ~160ppm chloride in it).
Matt,
Thank you for your response. I plan to refill my spa in a day or two. Once I get the salt level & my water chemistry back in balance, I will follow your suggestion & test 40ml of water with the K-1766 every few days (rather than the 10 ml I tested in the past). I will ignore the IC readout.
Here are a few additional pieces of the puzzle that might be useful:
1. For 30 days in July, I turned the auto fill off & used the K-1766 to test the water daily. I added no water manually. The daily test results remained in the 2,600 - 3,200 ppm range. During the same period, the water level fell 1/32" daily.
2. I then manually refilled the spa. If my calculations are correct, I added about 136 gallons of fresh water. For the next 15 days, the salt level remained in the 2,800 - 3,000 ppm range with the auto fill still off.
3. Finally, I turned the auto fill back on. For the next 18 days, the K-1766 indicted that the salt level fell from 2,400 to 1,800 ppm.
So, Matt, does this information trigger any particular thoughts regarding any leaks, evaporation or testing anomalies? Thank you so much!