refractometer?

[crister13]

I just got my refractometer, and tried to calibrate it. I used pure rodi water and adjusted to 0. I then tried it with salifert refractocheck rated for 1.026 and it came up as 1.028. Which should I trust?​

 

[melosu58]

Moved to General Hardware and equipment discussion.

 

[crister13]

Does anyone know? I think I should go by the rodi....... right?

 

[ccCapt]

No. Go by the calibration fluid. The proper way to calibrate is using a calibration fluid. A refractometer measure how much the water bends (refracts) light. Fresh water bends light differrently than saltwater, which is why the refractometer was off when you calibrated with fresh water.

 

[crister13]

O ok. Thanks!!!!! What should I do when I run out? I dont really want to repeatedly spend money on calibration fluid. How should I do it?

 

[ccCapt]

I don't know how much fluid is in the salifert refractocheck...and where did you get it? That's rarely for sale in the US and is usually only given away as samples at MACNA and other reef shows.
Anyway, it only takes a few drops to calibrate and you don't need to do it everytime you check your water. I bought a bottle of Pinpoint Salinity Calibration fluid a few years ago for around $6 and I still have it.
PINPOINT® Salinity Calibration Fluid - English

 

[crister13]

Ok thank you. I bought a refractometer on eBay and it came with it. The temp in my house doesn't fluctuate very much. How often should I calibrate?