Refractometer

[Pivitol]

I bought a $20 one off of Amazon and couldn't read it for the life of me. (Would not focus) Sent it back and bought a Milwaukee and haven't looked back, definitely one of my top 5 purchases for my tank.

 

[Randy Holmes-Farley Verified Community Expert]

What should this read

While it can be used, that one in particular doesn't really have the needed sensitivity.

Refractometers And Salinity Measurement
http://www.reefedition.com/refractometers-salinity-measurement/

Brix Refractometers

A commonly manufactured type of refractometer is called a Brix refractometer. Its scale usually reads in Brix, or % Brix (percent Brix). These refractometers are used in many industries to measure the concentration of sugar in water such as in the soft drink industry. They can be used to measure seawater’s salinity, but are not always precise enough around the range of seawater’s refractive index to be useful. A resolution of 0.2% Brix is common, and that is borderline acceptable for the reasons detailed below.

Table 4 shows the relationship between seawater salinity, refractive index and % Brix. If a refractometer has a resolution (not accuracy, but resolution, which is the finest amount it can distinguish) of 0.2 % Brix, then that translates to about +/- 1 ppt. So the best resolution would translate to 35 ppt seawater reading 34-36 ppt, which may be adequate for reef aquarists. A Brix refractometer that reads 0 to 10 % Brix with a resolution of 0.1% Brix might be a fine choice for determining seawater salinity in a reef aquarium, (although they are not inexpensive). Some Brix refractometers have a resolution of 0.5 % Brix or even 1% Brix, and they would not be suitable choices.