Salinity Measurment

[ReefDreamz]

Hi, I just received a new milwakee refractometer. I thought I was getting a deal when I bought it but it turned out I bought the model without automatic temperature compensation. The directions state that the water needs to be 68 F. To calibrate I used RO water at 68 F (I measured temp with a digital thermometer) I then measured some tank water cooled to 68 F and it read 1.029, then I read the tank water at the temp in the tank ~81 F and the refractometer also read 1.029 so there was no difference. Then I read the water with my swing arm hydrometer and it read 1.026. So my ? is which measurment do I trust. Any advice would be awesome.

-Cody

 

[terrymr]

Re: Salinity Measurment

<a href=showthread.php?s=&postid=9468131#post9468131 target=_blank>Originally posted</a> by ReefDreamz
Hi, I just received a new milwakee refractometer. I thought I was getting a deal when I bought it but it turned out I bought the model without automatic temperature compensation. The directions state that the water needs to be 68 F. To calibrate I used RO water at 68 F (I measured temp with a digital thermometer) I then measured some tank water cooled to 68 F and it read 1.029, then I read the tank water at the temp in the tank ~81 F and the refractometer also read 1.029 so there was no difference. Then I read the water with my swing arm hydrometer and it read 1.026. So my ? is which measurment do I trust. Any advice would be awesome.

-Cody

Given the sample size (a couple of drops) isn't the sample going to be at whatever temp. the refractometer is at anyway ?

 

[ReefDreamz]

You know I thought that too. I think the refractometer is at room temp which is around 73 F. But theres no way to get the actual refractometer to 68 F unless that happens to be the room temp. So all I could think of was get the water to 68 F.

 

[ReefDreamz]

bump

 

[terrymr]

Any experts want to chime in ?

 

[I am a giraffe]

Randy had an article on refractometers. A link to it is in the chemistry forum.

I think a point of it was that if you just let the sample rest on the meter for 15 seconds (might be 30), the temperature of the sample will match the meter and be adjusted for temperature.

 

[Travis L. Stevens]

Here are some really good articles that should answer most, if not all, of your questions.

Refractometers and Salinity Measurement
Temperature Corrections for Hydrometers
Chemistry and the Aquarium: Specific Gravity: Oh How Complicated!
Reef Aquarium Salinity: Homemade Calibration Standards
Lateral Lines: Hydrometer Observations Part I
Review of Hydrometer accuracy by Steven Pro
Discussion of said article.