So after seeing soo many reefers saying to use calibration fluid to set my refractometers I grabbed a bottle while I was at a lfs. Got home and made up a batch of water in a 5 gallon bucket. I don’t weigh anything, just drop pump and heater in and add a little salt, wait and check, add more salt, wait and check till it’s where I need it. Since I had calibrated two different refractometers with the pinpoint fluid I figured I had better double check the salinity with my tropic marin hygrometer and so glad I did. My hygrometer was reading 1.035 where as both of my refractometers read 1.026. My refractometers are one red sea branded and one no name petco generic. I then recalibrated both of them using plain rodi water and wouldn’t you know….they both match the hygrometer. Never again! They can stick calibration fluid where the sun doesn’t shine!