The Puffer Forum

Lately I've been using the refractometer at work (vet hosp.) to get a more accurate reading because I'm setting up a marine tank, and my hydrometer seemed way off in comparison! So I finally bought my own refractometer, calibrated it to distilled water, and compared it to the one at work which is also calibrated to distilled water at 1.0. I put a sample of my tank water on each, but got different readings! The vet's refrac reads 1.017, while mine reads 1.023. The one at work looks and feels higher quality, but the reading mine has is closer to what I would expect with the amount of salt I added. Very interesting though...

I read that the way you calibrate can make a difference. Though not by that much. They say if you are using your refr. for an aquarium, you should be calibrating with fluid that is conductivity: 53 mS, salt water specific Gravity: 1.0264 SG. The argument was that at this salinity it calibrates your refr. at mid level marine salinity range where distilled water does so at 1.0000 apparently making your refr. most accurate at the level it is calibrated for. Made sense to me but wether it holds true or not....Idk. Even calibrated with distilled it shouldnt be off by more than .0015 or so. Your difference in measurments is awful large.

That is odd, Jose is right, technically you should calibrate with the target salinity, you can find solution to calibrate online, check marine depot for calibration fluids.

I recently bought a refractometer from the LFS and it came with a target solution to calibrate the refractometer.

I got mine on Ebay for under $30 including shipping. I'll look into getting a target solution.