Salinity/gravity

[Dewey]

Ok my hydrometer reads gravity and my refractometer reads Salinity. What is the difference? This my sound like a stupid question but i can find anything in the books i have.



Thanks Dewey

 

[loganj]

Actually, both will tell you the same thing. I may be corrected by one of the scientists, but I believe SG is a measurement of density. The higher the salinity, the more dense the water. Salinity is the salt content. I would rely on the refractometer more than the hydrometer as long as you have calibrated it with distilled water. For a reef tank, salinity should read 35ppt and SG should be 1.024-1.026.

 

[reefrunner69]

but I believe SG is a measurement of density. The higher the salinity, the more dense the water. Salinity is the salt content

Totally true, the problem with specific gravity is other things in the water effect density, salinity is specifically the salt content, which is what you want.

Both are temperature dependant, but salinity is much less so than specific gravity, ie; there is not as big a change in a few degrees.