Refractometer question

[EvilE]

I recently ordered a salinity refractometer, and I am still waiting on it to arrive--I don't trust my swing arm hydrometer, so I borrowed our refractometer from work. It is a Total Protein/ Specific Gravity refractometer, mainly used for serum or urine. Would that refractometer properly measure the salinity of my tank, or are the refractometers different?? I guess what I'm asking is this one calibrated different from the salinity specific one? They both measure SG, but is the salinity SG different from the serum/urine SG?? The reason I ask, is that my plastic swing arm hydrometer is measuring my salinity at 1.023 and the refractometer from work is measuring my tank water at 1.018---HUGE difference!!!!

 

[Travis L. Stevens]

The refractometers are different and will give you an improper refractive index reading. Read more about them here.

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.

 

[EvilE]

<a href=showthread.php?s=&postid=9534432#post9534432 target=_blank>Originally posted</a> by Travis L. Stevens
The refractometers are different and will give you an improper refractive index reading. Read more about them here.

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.

Thanks--I've got some reading to do!!! So I guess, I'll go with 'ole swing arm till my salinity refractometer arrives......

 

[EvilE]

<a href=showthread.php?s=&postid=9534432#post9534432 target=_blank>Originally posted</a> by Travis L. Stevens
The refractometers are different and will give you an improper refractive index reading. Read more about them here.

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.

This article answered it!! Thanks again

Clinical Refractometers

Some medical and veterinary labs use a type of refractometer called a "clinical refractometer." These are normally used to measure proteins in urine, serum and other biological fluids. The scale can read in units familiar to reef aquarists (ppt or specific gravity), but that is ppt or specific gravity of a protein solution, not a seawater solution. Those units should be ignored, and if they are all that is available on the refractometer, I'd find another refractometer. Without a conversion table to seawater salinity or specific gravity, such readings cannot be used to gauge seawater's salinity as they will be way off. Some clinical refractometers read in refractive index, which is okay if you match the refractive index to the appropriate seawater refractive index (e.g., 35 ppt seawater has a refractive index of 1.33940). Such conversions of refractive index to salinity or specific gravity are shown in Figures 1 and 2, and Table 1.

 

[EvilE]

wow--great articles!!! It seems with the testing done, that swing arm cheapies are perfectly suitable for measurments!!! Once my refractometer arrives, I will conduct my own test!!!