Refractometer calibration?

[maximo]

How often does everyone have to recalibrate their refractometers? Lately I have been having to calibrate mine every time that I use it. I calibrate it using rodi water and adjust the screw until it reads zero. I calibrated it yesterday afternoon before I did a water change and I just checked it again this morning and it is reading off by a whole 5 ppt! This is telling me that it is time for a new one; mines is currently about 5yrs old. Has anyone had any positive or negative experience with the digital refractometers?


Thanks, Max

 

[Marshall O]

I use a standard refractometer, not a digital, but I calibrate every time I use it. I use 35ppt solution to calibrate it with. With the version I use, temperature of the refractometer itself can greatly affect how it reads.

 

[wrassefan]

I usually check it once or twice a yr using rodi or distilled. Mine usually only fluctuates +/- 0.001 but it is 10yrs old or more.

 

[dannyp02908]

Due to the way our refractometers read, calibrating with RODI is not recommended. There is an article somewhere that shows why.

 

[JohnK]

http://reefkeeping.com/issues/2006-12/rhf/

In short the slope of refractometer scales vary so it's best to calibrate with a standard that's the same or close to what we are going to be measuring.

 

[nemodan]

I have been calibrating my refractometer with distilled water, in lack of RODI water, as recommended by the manufacturer. I use Ocean water, and it is always 1025-1026. Meaning that the refractometer is working OK with my calibration system.

I Also observed that the Temperature was affecting the calibration. I had mine in the garage. Now is at the house.

 

[Ruge13]

Huh.... I have not re-calibrated mine since I bought it 4 years ago... guess I should do that.

 

[jason401]

I calibrate mine every time i use it with a 1.026 calibration salt water.

I do see it move on occasion, and I'm pretty darn careful with my measuring eqpt. Use it, clean it, put it away.

Mine doesn't measure and compensate temp

 

[dannyp02908]

I also calibrate every use. I use 35ppt calibration solution. I have tried zeroing it with water. Then placing 35ppt calibration fluid on it. The measurement was way off. No more water calibration for me.