Root life expectancy

[MT-Phal]

So I've had my phal in s/h for about a year now, and it is still slowly recovering back to it's old self. See prior posts if you want to see my s/h odyssey. Anyway, I have a handful of new growth that were doing really well up until last week. They were bright green with healthy tips. However last week one of them had a case of that spiderweb-ish mold, and the green velamen was slowly turning dark and black.

I cleaned the mold with a q-tip, physan, and plenty of h2O2, but now the root tip has stopped actively growing and the root is slowly turning dark. The root section before this growth, which grew into and adapted months ago to S/H, is also turning black as well. Do roots have an expiration date? Any ideas what could cause this to happen?

I flush every day, water at 150ppm with fertilizer bought from Ray.