I have an Apex and my salinity was off. I didn't realize it until I did my water change and checked it to my refractometer. Since then, I got calibration fluid and seemed ok for a week and now my salinity probe is way off. It keeps reading 27s when my refractometer (which I also calibrated) shows normal. I have only had the apex since Christmas. What would you do.
I always warn people that apex salinity should only be used for reference but is often not accurate enough to rely upon alone. Best to use it for warnings (ie ato sticks on or quick glance) but check against refractometer which should be used when doing any water changes.