I have a refractometer and swing arm. I use the swing arm when making up new saltwater until I get close then switch over to the refractometer for getting it the same as the tank.



However, when you are measuring an electrical current across the probes as is the case with a pH or salinity meter, it is a problem.
This kind of makes you wonder if you might need to take out the grounding probe and clean it off every so often.