Temperature and sg

[moseley75]

At what temperature should I set the sg of my water. I use a RedSea refractometer and calibrate it at each use. The test solution I have is always at 70°F. I tested the water I was using for water change and it was at 1.025 @79°F. When I took it to the LFS it had cooled to 70°F and they measured 1.027 w/ a Milwaukee electronic refractometer. I returned home and tested w/ my refractometer and got the same reading as the LFS. The Refractometer is supposed to be temperature compensated. I keep my DT at 79°F. Should I mix the water at 79° or 70° and at what sg? I use Aquaforest Sea Salt.

 

[Martin Kuhn]

Using a refractometer I recommend to use the salinity scale (psu) for reading, not the SG scale The given value is temperature independent which is an advantage. Typical level is 35psu (which ~ matches 1.026 SG at 26 degrees Celsius or the corresponding Fahrenheit value 79 F).
Anyhow .... the little amount of water that you put on your Refrak immediately changes to the temperature of the refrak itself.

Be sure to calibrate with a solution close to 35 psu (1.026 Sg at 25 degrees Celsius) not with 0 psu RODI

It doesn’t matter too much at which water temperature you „mix“ your saltwater.
A typical quantity is 41g salt per 1 Liter RODI to achieve 35 psu saltwater (155 g per 1 gal RODI)

 

[Randy Holmes-Farley Verified Community Expert]

At what temperature should I set the sg of my water. I use a RedSea refractometer and calibrate it at each use. The test solution I have is always at 70°F. I tested the water I was using for water change and it was at 1.025 @79°F. When I took it to the LFS it had cooled to 70°F and they measured 1.027 w/ a Milwaukee electronic refractometer. I returned home and tested w/ my refractometer and got the same reading as the LFS. The Refractometer is supposed to be temperature compensated. I keep my DT at 79°F. Should I mix the water at 79° or 70° and at what sg? I use Aquaforest Sea Salt.

If the ATC is functioning perfectly, it won't matter what temperature you calibrate or read at, as long as it is within the range of the ATC design.

If the ATC is not perfect, then it makes sense to calibrate and read at the same temp, whatever temp you choose within reason.