Salinity probes in general are pretty hit or miss. I've had one that have never been accurate, one that have been accurate for years, and ones that have been accurate for years and suddenly wildly fail. They also seem to read drops in salinity quicker than gains. Drops are typically seen in real time or pretty close, for some reason rises take a few hours to catch up. After a water change I typically plan on 24 hours for the probe to get back to reading right. Never use them to control anything, only for alarms. And if it alarms look everything else over and verify before freaking out. I will say that they have alerted me to stuck ATOs before, that's what I trust them most to do.