calibrated refractometer


New member
Buy a bottle of Pinpoint 53.0 mS salinity calibration fluid, put a few drops of it on the refractometer, then turn the adjusting screw until it reads 35ppt. I usually do this every time I do a water change since it's quite easy and it's almost impossible to use up an entire bottle of calibration fluid. You can also calibrate using pure freshwater, but it's not nearly as accurate at seawater levels. You should calibrate at the level you will be testing (35ppt in most cases).