Measuring Specific Gravity of 1.009

[FlyPenFly]

Trying to calibrate my refractometer to 1.009 for a Hyposalinity Qt tank. I tried the RODI method but not quite confident in it. I wanted to try this with calibration fluid set at 1.026:

Mix equal volumes (be very precise) of RoDi water and calibration fluid. That should give you a new calibration solution with 1.013. Use that to calibrate. Or you can mix 1 part calibration solution with 2 parts of RODI, that would give something like 1.0086. Again you need to be very precise.

So adding 1ml of calibration fluid and 2ml of RODI water should get me close to 1.009 correct?

 

[JimWelsh]

Yes.

The easiest way to think about it is to replace the "1." part of the SG value with "0.". Instantly, things become linear, with a y intercept of 0.0. Do your calculations, and then swap the "1." back in.

In your case, if you start with 1.026 water, then call it "0.026". A dilution such as you suggest would give 0.026 / 3 = 0.00867. Rounded, it's 0.009. Swap the "1." back in: 1.009.