Yes, given stable humidity~65% and temperature ~78°F constant light level, constant leaf surface area, consistent tent fan breeze, You are not replacing any nutrients or water the PPM will remain the same if the plant is using them proportionately. That is a lot of conditions to keep under control. I am not saying it cannot be done because it can in a sophisticated operation. Mine ain't that! Another problem in my style of DWC is that I never let the water/nutrient mix level drop and keep it constant at 1/2" - 1/4" below the net pot. This is accomplished using a float valve and a top - off tank. After the first couple of weeks when the plant gets bigger and starts using the nutrients PPMs start going down faster; I mix nutrients at 25% of the starting res numbers in the top-off. This is not perfect but it does keep you pretty close all week when it is time for the res change.