Digital salinity readings

[alanedinburgh]

Hope someone can shed some light on this for me.

I bought a digital salinity monitor and found the readings to differ greatly than my trusty refractometer. I seen on some Facebook group comment that if you are running two part dosing this can result in false readings.

can someone explain the logic/science behind this?
Thanks

 

[Daniel@R2R Verified Admin]

Which digital meter are you using? I have used Hanna and Milwaukee, and both of those were solid on readings. Also, how are you calibrating the unit?