I think that’s a Lostgirl hazard. In this case, I’m risking only a few scratches and play bites. 
I did. If you recall the Star Trek episode in which Scotty’s idea of fun was brushing up on his tech manuals instead of beaming down to the R&R planet like everyone else, that could be me. Except I’d smoke a joint while reading.
So if the water dept can tell me how much nitrogen and potassium are in our tap water, I can calculate its CEC. That would enable me to compute the desired ppm range for calcium and magnesium, using the table I posted above
But that would deny me the fun of calculating the amounts myself! 
(So I can choose a cal-mag product that best matches my numbers.)
What’s pHb, and why is nitrogen omitted from the sum?
That’s a much larger range than the table recommends, but I suppose we’d expect the range that has no detrimental effects to be wider than the recommended range.
How much per gallon?