Black spots on a Dendrobium and a Vanda hybrid

[camille1585]

Back in October I noticed the first black spots on both these orchids. They didn't seem to spread so I didn't think much about it. Fast forward to today, and there are now far more, and spreading to other leaves.

The Den is a Den Hibiki, and after killing several I finally have one that is doing really well for me and doesn't mind the heat (I ordered it from Italy this past summer, thinking that if they can grow it in their climate, it should do fine with me). I would really hate to lose my Hibiki....




The Vanda type is Vanda cristata x Ascocentrum curvifolium. I got it from the same vendor in the same order, but I don't think it's a vendor issue since both were super healthy on arrival.




I'm not sure why they got diseased, my humidity is generally pretty low (no more than 50-60%, usually around 30% this time of year).

What can I treat the plants with?