I agree that this could be a low salinity issue. I would suggest that you click the link I provided above and make your own calibration fluid, and then make sure your refractometer is calibrated. It's easy to make you own standard solution, practically free, and then you confirm or eliminate a low salinity issueIdk the brand but the reading seems right mathematically. The mag being that high and my fish and corals being seemingly happy also makes me think the salinity is good.

