Dd h2ocean refracotmeter

[Nathd2311]

I have a dd h2ocean refractometer atc. Instructions say to calibrate it to zero using pure water. When I do this and measure it against 35ppt solution it is off. Which should I use to calibrate? Rodi water or 35ppt solution. My refractometer says it should be calibrated with solution that is 35ppt at 20degrees but my solution is 35ppt at 25 degrees. Does this matter?

 

[ss30]

If you calibrate it with a 35ppt solution at 25 deg and your tank is 25 deg it will be fine.
It's best to calibrate it with 35ppt then you know it's right at 35ppt, I do the same

 

[Randy Holmes-Farley Verified Community Expert]

I've never understood the claim by a number of refractometer companies that claim to have an ATC (automatic temperature compensation) but then go on to say calibration must be done at a certain temperature.

I think they are just not understanding their own device, or possibly they do not have confidence in the ATC aspect of it and are hedging their bets.

Maybe they all just mindlessly copy and paste the same wrong directions some company posted long ago, perhaps for a nonATC refractometer.

 

[Nathd2311]

Thank you for the responses, I'll go off the 35ppt solution