First attempt at a 24-hour "Martian Method"

[Mother]

You have eliminated other variables so I'm guessing it's the water.
My tap water grows some black hairy yuck on roots.

It IS the water! I swapped out the water with some R/O water (you know the kind you get out of the "vending machines" in front of the grocery store?) and the plants are healthy and happy. There's still a snot buildup on the roots that I have to get rid of (pythium?) but I just picked up some strong H2O2 that will help me keep it at bay. Also, there is a burst of new, clean, healthy white roots growing out of the net pots now, and they'll be a good replacement for the old, long, stringy roots that have been battered by the root rot.

You're a great healer, Weez!