You should be equally concerned about the proportion and concentration of your nutrients. What balance are you using? If your EC is great and you have the wrong brix of nutrients what difference does it make? Your plants are grown enough to flower. Personally I don't worry about EC. I use a liquid style pH tester in an aeroponics system and am awaiting a harvest of an intensely frosty blue mystic plant using no CO2 and my own designed tub and system.