I've had some odd happenings with some coral, and in the process of narrowing down the culprit, I figured it was time to give the ol' refractometer some attention. I calibrate it every so often with RO/DI water, but after reading a few online articles, I was convinced that calibration with RO/DI water wasn't providing accurate results.
There are recipes to make a calibration solution at home... and in retrospect, that would have made a great DIY article... but I went the easier, more accurate route and purchased some American Marine Pinpoint Salinity Calibration Fluid. The calibration solution will allow you to calibrate to a higher point on the scale, which provides a better level of accuracy for the ranges we were commonly testing in.
The calibration solution will allow you to dial in salinity to 35 ppt, which is about 1.026 sg. To ensure better accuracy, I set up a "calibration station". I put warm water into a cup (measuring cup) and dropped in my handy dandy cooking thermometer (which I have calibrated recently). I waited until the temperature was about 80 degrees and dropped the bottle of calibration solution in there. When the temperature of the solution was at 78, I took a sample with a syringe and dropped a few drops onto the glass testing surface of the refractometer. (It's starting to feel like high school chemistry all over again). I closed the cover plate, and took a visual reading.
The reading was right on: 35ppt. "Wow," I thought, "that was uneventful." Indeed it was. I rinsed the refractometer with some clean RO/DI water and tried again. To attain a sense of satisfaction, I moved the calibration screw with a small screwdriver. I moved it up, I moved it down, and then I carefully dialed it back in. Rinsed it, and tried with some more solution (why not, I have a huge bottle of it). Bam. It was set. I tired with some RO/DI. Bam, set.
While I didn't have any "A-ha" moment with testing, it was certainly good to know my refractometer was calibrated accurately. A little insurance goes a long ways, and I now can calibrate my refractometer with a level of accuracy going forward.
Until next time...
