EC in, Flow rate/volume gives EC out , if the flow is not enough the EC out will rise, if irrigations are not frequent enough it will also rise.
Ive gone from Coco to RDWC and the first thing I learned is how they dont need high EC Im down to 350ppm mid flower and they happy over 400 they burn, had a crop finish at 5wks because the EC was 600 which browned the pistils off and stalled growth, the other thing Im seeing is they feed continually 24/7 , there is a sweet spot where the plants are in balance and your readings are very stable and this has to be dialed in for strain and environment, what numbers work for one guy can wreck another guys crop so be careful with what goes in the tank.
With Coco I ran 600 to 800 ppm and ran the flow rate to where the out equaled the in, and if it went up added more irrigation cycles, if it went down could lower the number of cycles or raise the EC a little.
Here is a great article with a lot of information on management of the nutrient system and how the plant uses it.