Brightwell Aquatics Aquarium Reagents Refractometer Calibration Same old is designed to offer a correct reference for the calibration of seawater refractometers, hydrometers and different density measuring equipment. 1.0264 Explicit Gravity 1.3394 Refractive Index 35 ppt Salinity 53 uS/cm at 25 deg c 250ml Instructions Shake product smartly before the use of. Clean Refractometer prism slide with fresh distilled water. Dry totally with soft clean dry cloth. Place a few drops of Brightwell Refractometer Calibration Same old fluid at the slide. Wait 45 seconds and calibrate to 35 ppt Salinity.