Update
The Black Domina plant still has the worst symptoms. I pruned her bad leaves until she looked 100% healthy. A few days later, the brown/black spots and drying out is returning to mostly bottom and middle leaves.
Hypothesis
There is too much calcium and magnesium in the water I use, causing a cal/mag lockout, no matter if I give it 'mag-i-cal' or not. I live in Portland and normally get water that is merely 4-13 ppm according to their report. However, we do seasonally use groundwater which is 85-100 ppm. I would bet we use groundwater during our wet winters, and that it Ca/Mg are a big part of those 85-100 ppm.
So I went out and bought distilled water today. I flushed the soil of the Black Domina plant using a gallon of distilled water. We'll keep an eye on her.
I used another cheap Ph tester to back up the results my 3 way meter gives me. The shitty tube/powder Ph test says my soil is 6-7 or so, about what my 3 way meter gives me. Thus, I have not added any of the dolomite lime stuff I bought, which would only make the soil more acidic.
After all this, I am tempted to try my hand at hydro/aero.
Pics upcoming. Right now, the plants are getting cold air, wind, and regular misting as a mite prevention measure. Best to be proactive and only use the neem when need be, since I can't afford anything else to use in a rotation with it.