Brassocattleya leaf turned brown from the bottom up before falling off
 

I got my Blc. Memoria Vida Lee 'Limelight' (Brassocattleya Binosa x Lc. Brazilian Treaure) on January 17th, it was described as a young plant about 2-3 years from blooming size. I gave it a few days before repotting it into a self watering pot (the kind with a cone that goes down into the water) with LECA. As of now I grow on a windowsill basically because it's too cold outside (this will change during the summer, moving outside) my weather station says the temperature has ranged from 68° to 79° and the humidity has ranged from 20% to 26% in the last 36 hours. I use RO water with a very diluted fertilizer (Jacks classic orchid special 30-10-10, lowest recommendation is 1/4 tsp per gallon and I cut that in half) I did a flush last weekend with plain RO water and then refilled the reservoir with my regular feed and a boost of calmag. I tested the PH and it was about 5.9 initially, tonight it's 7.13 (I expected the rise because of the LECA). Everything has been going very smoothly, the roots have remained green and hydrated and the leaves were all green and firm. Last night I noticed one of the biggest leaves turned a light green. Whatever happened, happened very quickly because tonight I noticed the bottom half of the leaf was a dark brown. When I went to inspect a little closer the leaf fell off the plant. The cane doesn't seem to feel mushy or anything and is still green where the leaf came off. The rest of the leaves are perfectly fine as far as I can tell. This is my first and only type of orchid in the cattleya alliance, I have heard that they sulk after a repotting but this seems a bit extreme lol. I tried to get the best close up picture of the plant that I could, if anyone can see anything that looks like it needs attention or you want a picture of something in specific of the plant, or you just need more information in general please let me know! Im also including a picture of the leaf that fell

I'm also noticing this, what appears to be white crusty stuff on some of the canes. Bugs, or mycelium?

Recognizing that it's very difficult to accurately diagnose such things via photos, I'd guess that's black rot, caused by phytophthora and pythium species, and - unless you water it allowing water to get trapped and stand in any pockets between segments or under old tissues - your culture had nothing to do with it.

Isolate that plant, away from any other plant.

Option 1) Pitch it now! If my guess is right, that is very contagious, and kills pretty rapidly.

Option 2) Apply a systemic fungicide like Banrot, or possibly Cleary's 3336 (thiomyl)

That was what I was afraid of. This morning I checked it again and the cane is now becoming soft and I am seeing more tiny black spots at the base of the leaves. I doubt I'll be able to find any of those treatments locally, do you think the plant will survive a couple more days if I order it? It does seem to be moving rather fast.
When I did the flush and feed some water may have gotten on the canes, but this time of year the humidity is very low and I have a ceiling fan on low 24/7. I don't think that caused it but it's possible. It's also been getting pretty warm in the afternoons, I think heat accelerates it. The research I was doing last night said this type of orchid is very susceptible to black rot. I'm about 90% sure that's what it is. What a bummer.

That's very surprising in our low humidity environment. Where do you get the RO water?

Hard to say. Fungus maybe? Doesn't look like mealy bugs right now.

I get it from a machine at a gas station. PPM is only about 60, not sure if that makes any difference.

If you only got the plant less than 2 weeks ago, you didn't cause the problem, and probably can't cure it. Can you return this to the seller, or at least notify them? Orchids don't do anything fast, including die... I think this one was already terminally ill when you got it.

I'm sure I can let them know, but because I've already repotted it and it's been in my care I highly doubt they will give me any kind of refund or replacement. I got it from Orchids By Hausermann. The majority of my collection has come from there. I have seen one youtuber who got an oncidium from them with fusarium, but this is the first 'bad orchid' I've personally ever gotten from them. Well, to the best of my knowledge anyways lol. I will shoot them an email, maybe I'll get lucky :D
I don't think anything I did caused this, whatever it is, but I guess I don't know for sure either. It's entirely possible the canes got wet and some water got under the sheaths when I did a flush and fresh feed last weekend. I guess I just expected it to dry out fast enough with the low humidity in my house and the constant airflow. If anything it probably was an existing issue and the extra moisture and heat accelerated it. I'm pretty bummed, I'm gonna order some fungicide right now and give it my best shot, for educational purposes if nothing else lol

---------- Post added at 05:25 PM ---------- Previous post was at 05:17 PM ----------

I've never seen them in person, but I don't think it looks like mealy bugs either based on what I've seen online. The white build up on the canes looks more like scale or a salt build up. It's crusty. It looks like mycelium big time. I read about it in one of the links in the sticky thread in here. It's the mold that contains whatever the fungus is that causes black rot. I have one Phal that has a build up like this on its roots I thought was a salt build up. I separated it from the rest and am keeping an eye on it now lol. It's been that way a while, but don't want to take any chances!

---------- Post added at 05:31 PM ---------- Previous post was at 05:25 PM ----------

Whoa...$80 to $100 for banrot? Is that right? I'm looking on Amazon right now because that's the most convenient for me and they typically get my stuff to me fast. Im open to suggestions though lol

If you cut off the bad area into good tissue so nothing infected is left, the plant should survive. I doubt this happened while at your place. I agree it probably arrived this way.