A bit confused about salinity measurements

[surlytx]

I've been using a refractometer calibrated with 35ppt calibration solution and showed my tank running a hair below 35ppt. Yesterday, I purchased a Hanna Salinity Tester (for easier reading). I calibrated it per instructions using the Hanna 35 ppt solutions. When I tested the tank, the reading was 31.8 ppt. I was a bit shocked.

I calibrated the Hanna again and tested- Same results.

I calibrated the refractometer with deionized water to 0 - no adjustment was needed.

I checked the refractometer solution and was bang on 35 ppt. Header scratcher.

I calibrated the Hanna again and no change to the results.

The difference between the Hanna and the refractometer is outside the accuracy listed for the Hanna. Any ideas on how to determine the difference?

 

[Randy Holmes-Farley Verified Community Expert]

You can make your own standards. One of them may be off.

 

[Cali Reef Life]

I would mix up a bucket with salt in it and measure what the level is with both. Do like 2 gallons exactly a cup or whatever your salts instructions are and see which one is closer. My bet is the refractometer is correct. I had an alk Hannah checker say my tank was 4.7 alk and it was 12.3. Caused a crash in my tank because I kept increasing dose. So I no longer use them but some are great maybe mine went bad after 6 months... Anyone on here can tell you a good and bad experience but sometimes its always best to double check. Another way is to test a sample and see if local fish store has something to test it to be sure.

 

[NotApplicable]

I had 2 “reference solutions” shipped to me with my Milwaukee refractometer. One read well under what it should have, the other read well over what it should have.

I ended up making my own solution, and it measured exactly what it should have. Those reference solutions are trash!

 

[MaxTremors]

I would trust the refractometer.

 

[Randy Holmes-Farley Verified Community Expert]

Here’s how to make your own:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[dadnjesse]

I tried the Hanna, never had any luck with mine. I use the VeeGee Refractometer.

 

[surlytx]

Here’s how to make your own:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

Thanks!