I think they are one and the same. Kind of like that watts and volts thing. Electrical conductivity (EC)
measures the total dissolved solutes (TDS) in your solution.but does not differentiate among the
various elements so while your EC may be correct the elements may be out of balance. That's why
you should change your solution every 4 or 5 weeks and more often if you suspect it is out of whack.
nutrient solution strength should be the same with your method as with other hydro systems.
Ron