[Stones]

To properly calibrate a refractometer used to measure salinity, you will get a much more accurate reading if you use the Pinpoint Salinity Calibration Solution instead of distilled water. Although it doesn't say it on the bottle, the Pinpoint salinity calibration solution is exactly 35 ppt.

When I first got my refractometer I used distilled water to calibrate it as well. After taking a reading from my tank it showed the salinity was 1.025. Two years later I purchased a bottle of the pinpoint calibration solution on advice from someone on RC. After re-calibrating the refractometer using the pinpoint solution, I checked my tank to see if the reading changed. To my surprise, the tank read 1.021. I never knew it but for close to 2 years I had been keeping my tank at only 1.021! The livestock didn't appear stressed ever but I noticed much better polyp extension and faster growth rates in my corals once I had brought my salinity back up to 1.025.

With all the things that can negatively impact the livestock in our tanks, keeping the salinity at near natural sea water levels is often overlooked. For the $5 it costs to get the calibration solution, its well worth it in my books.