Are the measurement lines correct on the Red Sea refractometer?

[undermind]

I just got some calibration fluid in my BRS shipment today (Refracto juice), and noticed something strange with the measurement lines on my Red Sea refractometer.

While the calibration fluid is at 35PPT / 1.0264 specific gravity, the measurement lines on the refractometer for these readings do not line up.

For example, if I calibrate to 35PPT, the SG is a few thousandths lower than 1.026SG. And conversely, if I calibrate to 1.026SG, It places the PPT at about 37.

This seems like a pretty big deal to me. I'm not sure which lines to trust. Couldn't find other threads about this, but wondering if it's a known thing.

 

[Big G]

Yes. Mine has the same lines. So I set the calibration to the side with the 35ppt using the calibration fluid, ignoring the SG for the moment. Then I ignore the PPT side when mixing salt or checking my tanks.

 

[undermind]

Yes. Mine has the same lines. So I set the calibration to the side with the 35ppt using the calibration fluid, ignoring the SG for the moment. Then I ignore the PPT side when mixing salt or checking my tanks.

Hmm... Wouldn't that mean that either the calibration or the salt mix / tank check process would end up being inaccurate?

Also, at the core of things, I don't even know how you can even calibrate properly, when the SG and PPT lines don't line up as they should. If you calibrate to 35PPT, that places the SG several thousandths away from 1.0264, where it should be when PPT is at 35.

It feels to me as though this refractometer is trouble, unless it can be shown which scale is correct (SG or PPT)

 

[fishyguy7]

If I recall correctly I was told that the lines do not line up and you can’t use the calibration like that. If you calibrate it too the 35ppt then always read it in PPT. If you want to read SG then calibrate it on the SG side.

 

[Westside Guy]

I just purchased the RS refractometer and came across this thread. I initially used RO/DI as instructed in the directions and calibrated it to zero and then used the 35 PPT calibration fluid and it read 35 PPT. Wouldn’t the SG be accurate at that point?