Edema?
 

Hello, my friends

Need your help to identify what's this spot.

First let me put this in context.

I really don't know what orchid this is. I think it's a xylobium but don't really know.
https://s1.postimg.org/30vusrt9cv/20171014_182249.jpg

After my suspitions of a spider mite infestation, based on the spots bellow, I decided to spry it with a solution of alcohol + dish detergent.
https://s1.postimg.org/89go84b9y7/20171014_182257.jpg

https://s1.postimg.org/3mv17f588f/20171014_182331.jpg

After the spray I've watered it with plenty of water to remove the remains of the solution from the medium (I didn't do it for the leaves). As a side note I've watered this plant the day before this treatment.

The next day I've noticed this spot which seems to be spreading (haven't confirmed yet). And there's another one smaller on the other leaf. It seems to be on the underside of the leaf (although it has reached the top side also).

https://s1.postimg.org/37nl7uolhr/20171014_181436.jpg
https://s1.postimg.org/4s0kt5rxxb/20171014_181509.jpg
https://s1.postimg.org/2exyby4233/20171014_181921.jpg

I would suspect a bacterial or fungal issue. (Maybe it got cold while the leaves were wet?) You can probably keep it from spreading by cutting out the big black spot and a margin around it, dusting with cinnamon on the cut edges of the leaf. Don't worry about damaging the appearance of the plant for the long term, it looks like one of the types that tends to drop old leaves anyway. (Whether Xylobium or one of the related genera, it's typical. Zygopetalum is in that group too. And has the same tendency to get little spots on the leaves )

I will confirm if it's spreading. If not I'll let it dry out.
If not, I'll cut that piece of the leaf.
In the meanwhile, maybe I could place it in a drier spot.

Well, it has been a little colder than usual (around 20~22ºC inside) and we are now starting to experience autumn temps so it's time to decrease watering frequency and let plants get natural humidity instead of creating it artificially.

It doesn't seem to be spreading that much, just a little bit on the lower side...
Comparison between yesterday and today.

https://s1.postimg.org/16dx0atddr/Be..._day_apart.jpg

Do you still think I should cut the sick portion?

I think just let it be... if it shows any place else or mushy then would be the time to get aggressive. It will probably dry.

I've put in a dry place (20% HR) so I hope it will dry.
I'll keep monitoring.
Thank you, Roberta!:)

It might be a Coelogyne. They are susceptible to all sorts of leaf damage. Once the leaf is damaged, if you treat with alcohol or soap, the chemical may spread through the damaged spot into the leaf and kill more tissue. I have seen this happen after spraying alcohol on severely mite-infested leaves.

I would leave the spot alone. I would pretend it's a Coelogyne and grow it like that.

I took another photo yesterday and the black spot is the same size while that halo disapeared so I think it's drying now.

I believe it was the alcohol the cause of it because it appeared right after the spray.
I need some sugestions about how to treat it for mites without damaging more.

Coelogyne culture is similar to Xylobium. I've been monitoring the environmental conditions trying to understand what's best and now I know it likes a lot of humidity, around 80%, lots of water in summer with good drainage.
In winter I water it once/week and it seems to rest because there's no activity. It's not deciduous.

The parts dying after spraying are already bad. Spraying only makes them apparent. I would continue spraying for mites with your mixture.

ES, I've followed your sugestion and kept spraying. Yesterday ir was time for a 2nd round. Half an hour later I noticed the appearance of new halos on three leaves, occurring mainly along the leaf nerves. So far it didn't developed black spots and the hallos seems to have disappeared.