Just calibrated two Refractometers

Any decent refractometer should read accurate from 0 to whatever.

And if frogs had wings......

 

Every measuring device has some error; the farther away from your calibration point, the less accurate it will be

Now some have higher accuracy than others, so it may not make a big enough difference over the scale. But the point is still the same.

 

I don't know the science and engineering behind it but BRS states with this particular Refractometer do not use RO water to calibrate. So what reason do I have to believe they are full of fluff?

 

See my response above These lower priced refractometers are just not accurate enough to calibrate at 0 PPT and then expect them to be accurate at 35 PPT.

 

So... the refractometer I have from agriculture solutions that had me calibrate with distilled water at 0ppt could be highly inaccurate compared to using a 35ppt calibration fluid?

 

No idea. Seems to me it is the same basic ATC refractometer that BRS, etc, sell. I personally wouldn't trust just calibrating it with RO/DI.

 

For the science behind it, have a read through Randy's article
Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com
Always, use calibration fluid, until you are sure RO water will also work.

 

here's my method to calibration of the cheap float type hydrometer. Borrow a few friends hydrometers and make up water to what you would think is 1.026 or whatever you like to keep your water at. Test the water with all the devices and if they all test to the same, just test the water with your meter and mark it with a marker regardless of the scale lol. Me personally I feel like refractometers can be hit or miss and too many factors affect them, this is prime example with calibration.

 

That makes no sense, unless the other instruments were calibrated with a reference solution. A refractometer is not "hit or miss" when calibrated properly. The solution is not expensive.

 

Agreed X10.