Yes, AccuraSea is what I found was the most accurate calibration fluid for the Hanna and my other devices. I know it sounds weird, since you would think the Hanna solution would be the best for the HI98319.Are you saying you calibrate your Hanna with the Accurasea?
Also, during my search for the most accurate way to measure salinity, I found and bought a VEE GEE STX-3 refractometer. It's very well made and viewing the scale is so much easier than the "normal" refractometers, and it gives accurate, repeatable results. I use this along with the Hanna to double check the reading periodically.