Aqua Craft Products Salinity Calibration Fluid 53.0mS / 1.026 SG, 2 oz. 60ml.

I used this on my refractometer and adjusted it by 0.001SG. Seeing the other recent review, now I'm not sure if I cant trust it. (Posted on 9/26/2018)

As mentioned, I had always used RO/DI water to calibrate and never had a problem and matched what others got. So I bought this to make sure I was doing it correctly. After I calibrated both of my refractometers they both showed RO/DI water as -2 points below zero. I knew something was wrong at that point. I ended up buying a digital refractometer and sure enough, this stuff is way off as seen in the photo below. It's a total waste of money and will have you running your salt levels 2 points higher than you want. All I can guess is that some has evaporated and as a result, WRONG.

http://img.photobucket.com/albums/v737/UltraReef/Public%20pics/IMG_5578.jpg (Posted on 9/20/2018)

I always calabrated my refractor with RO/DI water. Then I was told to use this. My refractor was off by a couple of points. What I thought 1.025 was only 1.020. Now my salt level is backup where it should be. (Posted on 7/21/2015)