Diagnose my roots... Please.

[opal]

It is not a root rot.

Older roots turning brown is just velomen losing its ability to suck moisture but is not a dead root. The root should not be cut as it still has the ability to push new roots from it.

Only mushy and shriveled roots should be cut off.

The reason for velomen turning brown could be either drying out or fertlilizer burn as you already said and it's hard to just guess which one is it. I'd recommend misting it more often and use less fertilizer just to be on the safe side. If you get windy weather often, then it might be low humidity. Where I am, when it's windy, humidity drops to 20-30% outside, while usually it's around 40-50%.

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