Do softeners with aquasensors, and water meters, just measure/calculate hardness that passes into the softener? Are the sensors part of the valve? Where and when exactly do they sense? I would assume the calculation needs to be adjusted periodically as the resin ages. Can an additional sensor of the same type detect if the softened water starts showing hardness? Can the sensor tell the difference between Ca/Mg in the water versus Na. How do the sensors actually measure the water hardness? (Something electrical I'm guessing. Is it just conductivity?) How accurate and sensitive are they when working properly?