Bran new apex just setup calibrated and installed , after calibration problems where fixed salinity was at 35.4 in solution,39.7 in my tank and now it’s droped down to 29 my Hanna checker says it’s exactly 35.2 and it was recently calibrated and using a refractomiter it looks to be 35 ish
The most common problem with the Apex salinity probe is trapped bubbles inside the tube. Put it completely under water, tip it upside down, then gently tap it until you see the bubbles escape.