Refractometer wonky??

[hunggi74]

I wanted to test my water parameters this morning. Started off testing salinity with a Vertex refractometer. Put my Rodi water in and noticed unit was out if calibration. Had to adjust unit because plain rodi was reading at 1.013 salinity. So recalibrated, and put in my tank water. Sure enough, water read 1.01 salinity. I know my tank water was at 1.025 two days ago after water change and I've got a tunze osmolator to keep it there. So what's up with my Vertex unit?? Thanks!!