Black spots & loss of all NEW growth on zygo

[Viia]

Apologizes in advance for the long post, but I could really use some help with my zygo. I have had this plant for about a year and a half now. It has never flowered and all the new leaves get brown spots and slowly fall off. The older bulbs and leaves that were mature when I bought the plant are in the same condition they were when I bought it. The new bulb it grew after I bought it is now bare after all the leaves developed brown spots that spread. The newest growth also has brown spots. There is new growth coming from the 1st leafy old bulb.

The photo is a bit old, but you can see how the brown spreads and then the leaf yellows. The yellowing leaves have all dropped since the photo and the new growth at the front is bigger but spotted (it basically comes out with spots).

It's in a medium light position on a bookshelf across from a north-facing window. I haven't repotted since I got it so I guess I should do that soon. The bottom is rocks and the roots are gray but solid looking. There has been no new root growth at the bottom. The top of the pot is coconut husk. I hadn't seen any root growth there until recently.

I used to dip into filtered water and then soak the pot for 10 mins once a week using leaf growth orchid fertilizer at recommended amounts 3 times a month (once a month was a flush watering). My mother (who manages to get the same exact type of plant to produce over 20 flowers at one time) uses the 10 minute soak method, but she says nurseries actually don't water, they just spray from the top. So lately I have started dipping it in filtered water and then dipping in fertilizer for a minute. I also spray the top of the substrate/roots of all orchids every day (it can get pretty dry in the South African summers). I can see that there is now new root growth at the top of the substrate. The bottom of the pot is fairly dry before watering.

So what do you think the issue is? Disease? Low humidity? Too much fertilizer? Too much water? Too little water?