SG measurement: ICP vs. TM vs. refractometer

[Gone Reefin’]

I have performed all 3. Popular opinion states TM hydrometer as the gold standard. However, in my case, it is the outlier data point. I have measured all 3 ways. Both refractometers consistently show 1.027, and both show identical reading against BRS reference solution. ICP results came back at 1.0275. The TM hydrometer consistently reads lower, at 1.025. This in an in tank measurement will all flow off.

Temp is 77.5F. I know it’s not a big difference, but I am targeting a higher SG and just trying to reconcile the discrepancy. Do I continue to trust the gold standard (figure of speech of course)?

 

[Randy Holmes-Farley Verified Community Expert]

Who did the icp? Maybe they used refractometer. lol

FWIW, while I think the TM hydrometer is a great tool for the money, it is by no means the gold standard. If a high quality lab wanted to measure salinity, they use conductivity.

 

[Gone Reefin’]

You may be right! Triton conducted the ICP.

However, according to the almighty AI, they use a calculation based on ICP readings of individual elements, rather than direct measurement of salinity or SG. Not sure if this helps to solve the discrepancy or not…or increase the reliability of the reading for actionable purposes.

 

[Court_Appointed_Hypeman]

I find the temp drop trying to use the hydrometer is crazy. By the time I drop it in the graduated cylinder, its already like 5 degrees cooler which when I was trying to use it, threw it off too much.

 

[RobertK]

You could test the accuracy of your hyrdometer and refractometers using Randy's DIY recipes for an SG standard (for the hydrometer) and refractometer standard (for the refractometer).

 

[Justfebreezeit]

I think the main advantage of the glass hydrometer is its consistency.