Help phalaenopsis declining without obvious reason

[Foxy2702]

I have recently moved on from Phalaenopsis and growing more unusuall type of orchids, but I have few left. I have been gifted a very unusual and beautiful phal but it is not doing too good. I have repotted and treated for fungal and bacterial diseases and yet it is still declining. Leaves are slowly wilting and roots are drying out. I suspect it is dreaded Fusarium however due to plant naturally having purple tinge to its roots, leaves and stem, I can not be sure. How does one check for Fusarium if plant is purple to start with. Please see photos and maybe someone can give me some advise as I really do not wish to loose it, however do not want to put at risk my more valuable orchids.