not exactly. not sure how you can have a rdwc that doesn't recirculate all the solution all the time? mine was 30 gallons so i mixed up my nutes for 30 gallons at whatever EC i wanted depending on size/growth stage etc.
the "why" for lower nute strengths is that roots are always exposed to nutes in dwc/rdwc so they can feed anytime they want. then compare to a ebb/flow or even a hempy bucket which only waters the root zone from 1 to 5 times daily. the plant will eat less frequently so you can up your nute strength. that make sense?
Yes it does. My nutrients solution does circulate full till 100% but I basically am saying what your saying your just making more sense lol. My thoughts are treat 20 gallons at half strength put in additional 20 gallons and ph it all but basically it's applying 1/4 strength to all 40 gallons I dunno it made more sense when I typed it lol