Good Morfnoevight All! EO.
Pinky this is a possible sign of serious heart problems, I would get a doctor involved if you already have not.
Yes, think about what is going on, the plant will only take in a small amount of nutrients compared to the water it uses and transpires into the air. I have had plants use well over a gallon of water a day. Removing the water from the reservoir will concentrate the remaining nutrient ions causing the measured PPM to rise sometimes dramatically. This will present a solution to the plants on the next fertigation that can be much too high and will burn or even kill the plant. You want to replace ALL of the water the plants are using, this will prevent the concentration of ions. Now you will be able to watch the PPM of the solution go down as the plants use them. Without expensive lab equipment you cannot know which ions are being used up. This is why I recommend a reservoir change after a 100 PPM drop. Depending on the nutrient line you are using this can get quite expensive and the reason I spent so much time developing a schedule with the least expensive nutrients I could find.