Refractometer and Salinity Pen Readings With Tank Water Only

[sayurasem]

Hello, I’m having contradicting readings of my aquarium water salinity. Using the Hanna salinity pen its reading 1.026 SG, while a refractometer reads 1.029 SG. Water sample was isolated while performing the test. I tested freshly mixed saltwater with both salinity pen and refractometer reads the same salinity. Is there an explanation for this?

 

[Randy Holmes-Farley Verified Community Expert]

Hello, I’m having contradicting readings of my aquarium water salinity. Using the Hanna salinity pen its reading 1.026 SG, while a refractometer reads 1.029 SG. Water sample was isolated while performing the test. I tested freshly mixed saltwater with both salinity pen and refractometer reads the same salinity. Is there an explanation for this?

Might be lack of temp corrections. Which exact devices?

 

[sayurasem]

Might be lack of temp corrections. Which exact devices?

Temperature of water sample taken was 72F. Refractometer is a no name brand (ATC?) comes inside a blue case. Salinity pen is Hanna.

Edit: salt mix being used is regular Instant Ocean

 

[exnisstech]

I have two Hanna and both read 0.002 low if I calibrate with their fluid. Not sure why yours read the same in fresh salt mix. How are you calibrating the refractometer. I've been using one of the cheap ATC from Amazon for 8 years and it's been great. I use Randy's diy calibration fluid and verify with a TM hydrometer. I rarely test my mix or tank water with two devices for obvious reasons .

 

[sayurasem]

I have two Hanna and both read 0.002 low if I calibrate with their fluid. Not sure why yours read the same in fresh salt mix. How are you calibrating the refractometer. I've been using one of the cheap ATC from Amazon for 8 years and it's been great. I use Randy's diy calibration fluid and verify with a TM hydrometer. I rarely test my mix or tank water with two devices for obvious reasons .

I use RODI to calibrate the refractometer. For Hanna, I use their 35ppt fluid that came from the box. I noticed new Hanna salinity pen comes with 5ppt fluid which I don’t know what its for.

 

[exnisstech]

The refractometer should be calibrated with calibration fluid. The only way I can get my Hannas to read correctly is to calibrate them in saltwater known to be 35ppt I use 1.026 but that's just me. I thought the first one was junk because it always read low and bought another and it too reads low exactly the same as the first.
Here is Randy's article with the recipe for calibration fluid using table salt.

https://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[sayurasem]

The refractometer should be calibrated with calibration fluid. The only way I can get my Hannas to read correctly is to calibrate them in saltwater known to be 35ppt I use 1.026 but that's just me. I thought the first one was junk because it always read low and bought another and it too reads low exactly the same as the first.
Here is Randy's article with the recipe for calibration fluid using table salt.

https://reefkeeping.com/issues/2004-06/rhf/index.htm

Thank you!