RO water, EC readings, and mixing nutes - procedural question

After several seasons outdoors, I am in the process of setting up my first indoor grow running DTW in coco and have a question about calculating nutrient levels.

A few weeks ago I picked up a Bluelabs EC pen and have been playing with it. My drinking water comes from a whole house RO system with a 250 gal tank in the basement (raw well water has salt, manganese, calcium, iron, hydrogen sulfide, etc). If I test the product water, I get an EC reading of around 0.2 to 0.3 (170ppm on the 500 scale). I understand that trace minerals are helpful for plant health, but what is left in the RO product water are likely not the NPK sat building blocks they require for health growth.

Presuming I want to mix nutrients (H&G Coco A & B in this case) to hit a specific target, do I use the initial EC reading as a "zero baseline" and mix to hit a target that has an EC reading greater than what I really want?

For example,

Initial EC reading of RO water = 0.2
Desired EC reading of nutrients = 2.0
Add nutes until meter reads 2.2

I am probably over thinking this and should be reading the plants, but also want to understand the process as it should be employed.

Thanks!​