I only test it when I'm making water for a water change. My controller has a probe for it, I don't control anything with the reading. The readings are usually what I expect., when they are wrong, it's a probe error (air bubble, detritus, etc.) and not an actual change in salinity.I am not sure why so many people are focused on salinity. It isn't that important and fish and corals can and do live in a wide range of salinity.
plus you can calibrate it with RO which is nice. When doing anything major to the DT I just take a few drops from the ATO, calibrate it and run a testI use a Milwaukee MA887, only time it has off readings is if there's a bubble in the sample well or a lot of ambient light. I dropped it and cracked the display but it still works!
I do it backwards... my Milwaukee verifies my apex. but while mixing salt its just the Milwaukee. I do a max water change of 10-20% so if its off a little it doesn't really matterI have a Milwaukee also but I am thinking of picking up a Hanna also just to verify results.
That is because the VeeGee is calibrated at 20C. All calibration fluids I can find are calibrated for a refractive index at 25C. RI changes with temp so at 20C the fluid will be off. However, I have found this difference to be very minimal but might be different across fluid manufacturers.The Vee Gee seems to be working. It's definitely consistent, it just doesn't match my calibration fluid. The calibration fluid could be off though.