Everything that is in your solution counts toward your target PPM. That's why it's your target. A target isn't something that you try to achieve, but it's OK if you go over by 30%. No, you actually want to try and achieve your target. That includes additives, nutrients, whatever comes out of your tap, fly poop, etc. Your tap water may contain desirable nutrients, especially if it's well water. Copper, iron, zinc, all sorts of crap that the plant can use, and some of which it actually needs. You've gotta count this stuff.