Are we talkling hydro, or soil? If hydro, It depends on what your ppm numbers are. If your ppm numbers are going up, then your plants are drinking more than they are eating, and you should only add water. if your ppm numbers are going down, then they are eating more then they are drinking and you should add nutes.
If you are growing hydro, what type DWC, Ebb And Flow, Drip? If DWC, let me know, and I will explain how to figure it all out and add the nutes back. (do NOT ever add nutes directly to the DWC res, it can kill your plants)