Even when I first started doing DWC I didn't change nutes in veg. Just added more to raise the ppm as they got bigger. I would mix up a fresh, stronger batch when flipping to flower then started waiting until after the stretch to do a fresh batch until I finally let one go the whole grow without changing nutes and it worked fine. The last 15 tubs worth I never changed at all.
Salts don't build up in DWC unless you're adding more all the time and never checking ppm. You test ppm and just add enough to get back to your target range as they grow or raise it higher if they are eating lots more like they do during the stretch. With RO water and AN pH Perfect nutes I never once checked the ppm either.
Flush perfectly good nutes down the drain if you want. The guys who make them want you back as often as possible.
I've moved on to semi-organic growing in pots but will probably do more DWC in the future. It's fun until it isn't.
Good luck!