Here's how I see it, but I'm no expert.
You guys are over simplifying and over complicating it at the same time a bit in my opinion. Not being negative at all, just trying to point you in the right direction.
Look into valence. It will give you the exact understanding of how nutrients are exchanged, how they bind one another, how they bond to mediums, etc.
That's why I always suggest getting individual ppm of each nutrient so you can control exactly what your plant is getting and there's no guessing. Sure it takes time, but it pays off if you have an issue.