Small dark spots on Dendrobium Phalaenopsis leaves

[Jlin]

Hi!
I have this Den Phal for 2 years now, and it has grown a nice new Pseudobulbs this season. But I noticed some spots on the leaves of the newest and the other growths. Not sure whet these can be, and how to treat it... any thoughts? Maybe Bacterial Brown Spot or Leaf Spot?
I live in Canada so I’m not sure what product I can use - we don’t have systemics.

Additional culture information: It spent summer outdoors (which explains the big brown patch, this is a sunburn) but I moved a month ago and it is now growing indoors under lights. I don’t see spots on other orchids near this plant. Temps vary between 23 and 28C And there’s a fan running all day, everyday. The roots look really healthy to me, but maybe the media doesn’t dry out entirely in between watering.

Thank you!