ppm/ph issues, concerns

I have somewhat of a concern more than a big issue. I have been using aqurium ph up/down i notice that this rises my total ppm, for example after mixing nutes i end up with with about 580 ppm (veg stage) and ph of about 6.7 so i add couple drops of ph down to bring it down to about 5.8-6.0, now when checking my ppm again it shows roughly about 612ppm. will this harm my plants? i have read about salt builups if ph liquid contains certain chemicals...
Another question, my tap water is about 40 ppm is this good? i have a zero walter filter that can bring my water down to 0ppm, but do i really need to?
thanks guys, any help will be recognized with rep.