Refractometer question

[Thub]

Hi guys, it appears I got a 'saltwater' and not 'seawater' refractometer, because 35ppt and 1.026 dont line up. It lines up more at 36.5ppt/1.026. My thinking is that this really isn't a problem as long as I calibrate to 1.026 SG and ignore the ppt side of the scale.
I used a DIY calibration solution based on a post from Randy Holmes-Farley, which says that 36.5ppt NaCl is equivalent to 35ppt seawater, which is also how I noticed the scale discrepancy.
Is my thinking right on this or am I dooming myself to be forever off by 1.5ppt on salinity?

 

[Retro Reefer]

Just calibrate it with 35 ppt solution and ignore the specific gravity

 

[Randy Holmes-Farley Verified Community Expert]

Hi guys, it appears I got a 'saltwater' and not 'seawater' refractometer, because 35ppt and 1.026 dont line up. It lines up more at 36.5ppt/1.026. My thinking is that this really isn't a problem as long as I calibrate to 1.026 SG and ignore the ppt side of the scale.
I used a DIY calibration solution based on a post from Randy Holmes-Farley, which says that 36.5ppt NaCl is equivalent to 35ppt seawater, which is also how I noticed the scale discrepancy.
Is my thinking right on this or am I dooming myself to be forever off by 1.5ppt on salinity?

that is correct. Calibrate with a 35 ppt standard to set either 35 ppt or 1.0264 and just use that side of the measurement.