Refractometer v Hydrometers

I have two glass hydrometers. They both read the same level of salinity in my tank. I have brought in a couple water samples to the LFS to have them double check salinity. Their refractometer says that my hydrometers are off by 5 points. I've checked the hydrometers in distilled water. They were not off by 5 points.

Is the LFS refractometer not calibrated?

Should I trust my hydrometers?

 

Did you adjust for the temperature when using your hydrometers?

 

Personally with the cost, ease of use, and accuracy of Refractometers.. I wouldn't bother with Hydrometers ever again.

Have a sybon brand refractometer and love it.

 

I would assume the lfs was off. Not really a big surprise that they would not calibrate it right.

 

After adjusting for temp there is still a .003 difference. Could both hydrometers be off by the same amount?

 

It's not a good idea to make sweeping statements. I calibrated both refracts weekly with distilled water as well as the industrial spectraphotometer and the pH meter.

It's a possibility. However, another possibility is that the fish store calibrated theirs using their RO/DI water and they haven't changed the filters/resins in their filter and theirs is off.

 

I have a refractometer for brewing so I know how much better they are . I just have to find room in the budget for one.

 

I Didn't know that would effect the calibration so much. There is another LFS in the area that I can have check for now. Looks like I'll have to get a refractometer and calibrate it to be sure.

Thank you!

 

first make sure you shake the hydrometers up real good, to make the swing arm loose. then take the measurement.

Now if you go to this other store and it is the same reading as the first lfs. There reading is probably right. take note of the difference between what the hydrometers say and the refractometers say. adjust your hydrometer readings to compensate for the difference. Congrats you now have a accurate hydrometer method of measurement.

 

Both are glass hydrometers. I had a swing arm, but I returned it. It was a PITA to get a reading and was terribly inconsistent.

Good idea. I can take the same sample to both stores.