i just found a reply from hanna regarding the differences between conductivity probe vs refractometer. So based on understanding, it concurs to what you and me experienced. The refractometer might give inflated values compared to conductivity probe due to organics that contribute to the additional light bending but would not contribute to additional salinity. I also read that one cannot use the standard calibration meant to calibrate refractometer for salinity probe/pen calibration. My recommendation is just to stick to one, if u prefer refractometer just stick to it. For me, i more lazy prefer to use the pen haha. Maybe other experts can chime in. From Hanna instruments reply What is better for salinity? When comparing conductivity to refractometery to measure salinity, the consensus among the scientific community favors conductivity. This is because there are non-conductive material which can impact the refractive index of seawater but not the actual salt concentration. For example, if we add sugar to artificial seawater, we will see that our salinity value will increase but we have not changed the concentration of salt in the water. If we measured the salinity of that sample with our HI98319 conductivity meter you’ll notice the value is largely unchanged. It is common to have inflated values with a refractometer due to the large number of materials which will affect the density of that water outside of the dissolved salt values. For example, organic waste, sugars, potential non-ionic contaminants or uneaten fish food can increase the values produced on a refractometer but this would be less likely to occur on a conductivity meter like the HI98319. Sent from Singapore Reef Club mobile app