Did I over-fertilize my Lepanthopsis?

I posted this question on another forum but am not getting any response, maybe someone here will have some advice:
The Lepanthopsis on April 3rd:


Today:



My Lepanthopsis astrophora 'Stalky' recently went into a rapid decline and is probably dying. The only thing I can think is that I fertilized using Schultz Orchid Food 19.31.17. My fault, I didn't measure the amount - I put a few granules into a 1 cup spray bottle. I usually fertilize around once a month, and I thoroughly wet first with pure distilled water. I fertilized all the orchids in my terrarium this way, including a number of pleurothallids, and the rest are all fine.

The Lepanthopsis was thriving, had just grown around 10 new leaves and 4 or 5 spikes. It started dropping the new leaves first and the spikes have all blasted. Also, all the moss growing in the pot with it has turned gray - I believe moss is pretty sensitive to fertilizer.

Other condition considerations: good ventilation and air movement, 65-90% humidity, potted in sphagnum and never allowed to dry out, temps between 55 and 80, and no other conditions have changed since it was thriving. The black spotting on the old leaves has been there for months, although it may have gotten worse.

In the same terrarium, I have a Masdevallia coccinea 'Dwarf Pink' that occasionally develops brown, sunken patches on an older leaf. I suspected something fungal and have been removing affected leaves and spraying Physan. The Masdie is constantly putting out new leaves and has three buds, so otherwise it is very healthy. I also just removed two leaves from a Dendrobium cuthbertsonii that had suddenly developed two perfectly circular, sunken yellow rings. Hoping that isn't viral. I have no idea if all these problems could be related - they don't look similar.

Is there anything else likely to have caused this? Fortunately if it was the fertilizer, that is easy to remedy next time around.

 

Thanks for your response!

I fertilized a few days before it started dropping leaves. The fertilizer can only have been around double strength at most, based on my calculation after the fact. There are two Pleurothallis plants and a Masdie that all were fertilized at the same time and are fine.

Would false spider mites cause apparently healthy new leaves to drop suddenly? The black spotting was only on the plant's older leaves, which are now the only ones left.

I can certainly let it dry out a bit between waterings, but I was on a consistent schedule of twice weekly watering for months, which in my humid environment allowed the sphagnum moss to go from wet to damp. It was apparently thriving with that watering regimen.

 

Well, the general consensus seems to be that I was overwatering it, which makes more sense with the sudden leaf drop than over-fertilizing, I think. I took it out of the pot today and the roots weren't rotten, but they were light brown and a bit soft, and I did see some green stuff that looked like mold. I trimmed off all the dead stems, pulled off most of the sphagnum, and mounted it to the coco fiber/great stuff back of the tank. Hopefully it can recover with the four leaves it has left.

 

There is a circulation fan on 24/7, and a ventilation fan that turns on and off during the day to bring the humidity down to 65% (alternating with a humidifier that brings it back up). I have a Begonia pavonina in the bottom of the tank which is notorious for having leaves that spot and "melt" with poor air circulation, and its leaves are fine, so I don't think circulation could be the problem.

I'm going to leave it mounted and just hold off on fertilizing entirely for the time being, and see what happens.