If the EC is too high, I understand that it can be lowered by adding water with a lower EC, but wouldn't that reduce the amount of nutrients too much by diluting it with new water with a lower EC??
It would dilutes your ppm yes - if you have a 500ppm solution 1L and add more water your ec and ppm will drop (as long as your water going in is of a lower ppm). But the same amount just not concentration of nutes will remain.