I finally installed my ATO on my reef this weekend. So I have been monitoring my salinity daily. I almost made a huge rookie mistake today. I came home from work and found my ATO had used 2 gallons of RODI just today so I grabbed my refractometer and my tank was reading a little low. I started wondering if the sensor had moved somehow and topped off to much water. And the it hit me like a hammer, I couldn’t remember the last time I had calibrated my refractometer. Maybe 2 or 3 months? So I grabbed the calibration fluid and for the first time in three years it actually was out of calibration. It was showing the exact same as my tank with the solution. I calibrated the refractometer, checked it a second time and then rechecked my tank. The tank salinity was spot on and I’m so glad I didn’t make any adjustments before checking.