After your response I agree, over watering is more or less ruled out.
I'm going to spend some time researching as I'm curious now and if I find anything I'll definitely inform you. As far as I'm aware Oceans Forest is a very solid base, and with everything you've said now it seems doubtful to be a simple answer. To be blunt, with all that you've said if that was the case it seems like you would have found the answer and corrected it by now.
What does your RH typically sit around - I see in one of the pictures it's at 35%, is that about average? I ask because a few days ago I read about a type of fungus similar to PM that can cause more or less the entire range of symptoms from what I remember.