Dendro with spots

[SundayGardener]

Hello,
This dendro is finishing its blooming cycle. It was looking good then the leaves started developing spots, turning yellow and dropping. It is not in a high humidity area. I do have it isolated from other orchids.

Thinking at first that this was some sort of bacterial brown spot, I treated the spotty leaves with Physan. I know the pictures don't necessarily look like brown spot, but what I initially saw was just dark spots on leaves with the spots getting larger. Physan on the leaves that looked diseased didn't help and it spread further on the plant, which I have now sprayed in its entirety with Physan.

Should I be using a different product? So far, my biggest issue has been root rot, but now I seem to be branching out and exploring all the other ways that an orchid can be taken down. Speaking of which, is Physan appropriate for Anthracnose? Several oncidiums have browning leaf tips...but it certainly hasn't been warm here.

That link at the top of the page to different diseases is very helpful but I might be projecting hypochondriac tendencies on my plants. Except the dendro, something is definitely off there.

Thanks!