Phal Bellina Yellow Spots

[Manu]

Hello everyone.

I have a Phal Bellina that has many yellow spots. It started this fall and only got worst since.

I've inspected the plant thoroughly for pest and can't find anything. I do have predatory mites (hypoaspis miles) and some springtails, occasional fungus gnat in my Catasetums in the summer.

The plant is mounted on cork with some sphagnum Moss. I've cleaned up the mount a few weeks ago while inspecting it. Removed old Moss and added some fresh moss. Didn't notice anything bad there. Has full of healthy roots. It's also growing new roots and a new leave which is currently showing no spots. The previous leave that grew in fall up to January was fine initially, but now shows some marks which are different then the yellow spots, I'm thinking this might be due to low humidity in our winter conditions.

The only thing this plant suffered is a lack of light which is now resolved. I had to relocate my plants as my previous growing space is now my son's room. It had very low light from November to February while I was setting up the lights. All other plants I have suffered the same low light conditions but did not exhibit any such symptoms except slowed growth.

I've performed Agdia Virus tests for Cymbidium and Odontoglossum viruses which came out negative, but very well know it could be many other viruses.

I've attached 4 pictures showing the evolution of this from this fall up to today.

First picture is from October 31st. You can see minor yellow spots on leaves and the spike. At that time the plant was getting decent light conditions but might of suffered a brief cold breeze here and there.

Second Picture is from January 6th. You can see the spots increased in size. The new leave grew nicely but starts to show a few pits here and there. At that point plant was getting close to no light and also low ambient humidity (roots were well watered but RH between 30-60%).

Third and fourth picture are from yesterday. You can see how bad this got. The newer leave is full of pits. The one before is 75% yellow spots. Oddly, older leaves show way less yellow spots (has some but really minor). The new leave that is currently growing has no spots but is still very small. There is also small brown dots on the yellow spots.

I really don't want to trash the plant, but starting to think this might be the safest thing to do for the rest of my orchid collection.

Any thoughts? Advice? Someone encountered similar spots etc?

Thanks in advance!
Emmanuel