I have had a few leaves look like that. Since it only seemed to be the older lower leaves i believe it was caused by pH fluctuation. So i removed those leaves and i have kept a closer eye on pH, making smaller adjustments more often and i haven't seen it come back yet.
The B52 will definitly discolor your roots, and i have had similar concerns, but they were never slimey or smelly. i even rinsed them off after a water change once to be sure. But the Voodoo Juice seems to really be doing the job! Good Luck!
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