Pitting on Phal leaves

[camille1585]

A lot of my Phals have strange pitting on their leaves. It started about 2-3 years ago, right around the time where my Phals were subjected to a lot of neglect, so I'm guessing some opportunitic fungus got a foothold in my collection. The problem partially went away with good, regular care of the orchids, but it's still there, lurking, and afflicting a lot of the new leaves, especially in the winter.

My first guess was spider mites, but wiping with a cotton doesn't show tell-tale residues on the cotton. My second guess was possibly virus since I also had a mealie bug problem during the period of neglect. But even new Phals are getting it, that are on a different shelf (in the same room), and never had any contact with the infected Phals. Everyone is watered separately, and I sterilize tools/pots when repotting. I never get water on the leaves, and it's never cooler than 17-18C (roughly 60-65F), so I don't think it's mesophyll cell collapse either. And no other genera are afflicted, it's only the Phals! My Phal. equestris and equestris primaries seem less affected though.

After a few years of this I think I see a pattern: it's worse in the winter, and in spring/summer I hardly see any new spread.

The obvious solution is to stop buying Phals, but those are my favorites and do exceptionally well for me.

Any ideas on what this may be and what can be done about it?