This is gonna be very strain dependant. But that's the nice part of having the ppm/tds/ec meter. Your strain will "communicate" with you through this instrument to let you know what ppm it likes.
Basically, when your ppm drops, your plant is using the nutes you gave it and is going to be able to take a higher ppm (increase this gradually though). If the ppm raises upon testing, it's not using as much nutes as it is water and you may need to back off the nutes a little.
The idea will be to "push" the strain to find what weeks to add the max tolerable ppm and keep a record of this. Then, you have your ppm chart for that strain and can reproduce this with each grow.
Try to get yourself a schedule of checking ppm. I did mine daily and made necessary adjustments as needed (ie added nutes when ppm declined, added water when ppm went up). It works wonders and is one of the great advantages of growing hydro.
Hope this helps and great grow btw.
-Butters