Terrible advice! LOL.. If you ever do that, PLEASE send it to me before throwing it away. I've been using them since they were first released and they have always pretty much been spot on for me when compared to my refractometers. I've also installed plenty of them on other tanks and NEVER had a single issue with them! Not once and they are always pretty darn accurate.
A couple comments for the OP. First, you should leave the probe in the tank for several days before calibration. As mentioned above, placing the temp probe in the calibration solution when you do the calibration is very help. I just soak the packets in my sump for several minutes before calibrating. I place the calibration packet in a glass of tank water during calibration being careful not to get tank water in the solution. This insures the calibration solution stays the same temp as the tank water and eliminates the need to place the temp probe in the solution. FWIW, if the cal solution isn't the same temp as the tank water, the temp probe should be in the cal solution otherwise temp compensation will be off and the salinity reading will be wrong.
The CondX probe should always be placed in a dark area of the sump devoid of micro bubbles. Dark is so algae doesn't grow on the probe. This goes for all probes as air and or algae will effect their accuracy. Soaking it for several days before calibrating helps insure the probe is somewhat broken in. These probes are shipped dry. How important soaking is may be debatable but I have found better initial accuracy after calibration when this is done. Lastly, never run probe wires parallel to power cords. Keep them away from pumps too.
As for your refractometer, calibrations should be verified regularly. Some refractomters hold calibration very well while others loose calibration very quickly. I also suggest keeping the refractometer at room temp and having the refractometer calibration solution at the same temp as the tank water for best accuracy. Always be sure to use cal solution designed for refractometer use and 53000ms cal solution designed for probes. They are typically 2 different types of solutions for different uses. That said, your refractometer is likely way off if its been that long since you calibrated it.
As other said, the salinity probe should not be used as the only point for salinity checking. It should be used for trends, warnings and failsafes. A properly calibrated refractometer should be your number one tool for verifying sanity.
