Antelope type dendrobium has yellowing leaves
 

Hello all,
I have an antelope type dendrobium that I got recently that has been getting small black spots on its leaves. The leaves in question will then turn yellow and fall off. It is a beautiful plant with a full healthy flower spike but has been losing about one leaf a week.
The care I've been giving it is:
Near a south facing window out of direct sunlight.
A long drink about twice a week when the medium is dry
Fertilized twice this month.
I've attached a picture below. I would really appreciate any help you guys would be willing to offer, I love this orchid and would hate to lose it.
Thank you in advance!

I love these Dens but they really do have sensitive leaves. I’m not 100% sure why these happen and there could be a few reasons. When I do get these marks on my Antelope type Dens it’s because it’s been under watered (from root loss or from just needing to be watered more frequently). I’ve found these to be water hogs once the weather starts to warm up and don’t necessarily want to dry out

It could also just be the change in the environment if you just got it.

If it keeps happening (leaves yellowing and falling off in succession and doesn't appear to be stopping), then check the roots of orchid ----- all of the roots.

Also, check on the growing temperature range, and lighting level, and air-movement. Gentile air movement around the plant and through the media can cut down on fungal/bacterial activity.

Also check on watering method. And consider what media is being used.

And - stock some accessories, such as cleary's 3336 and agri-fos, which are systematic fungicides. Mancozeb (non-systematic fungicide) should be stocked too.

Also - make sure the amount of fertiliser being applied is an appropriate amount (not over-done).

I don't know what your dendrobium is. I grow a discolor in full sun, which stays in its spot permanently - and this particular one growing in the tropics seems to be able to just survive without any human intervention. The conditions here allow it to grab water directly from the air. Humidity is good enough to support it here in my region. I know that the discolor can handle a real beating from the environment. Click Here. This one grows in scoria (lava rock). I think it even grew out of one pot and into the pot next door to it (which wasn't even purposely placed there hehehe). It has never been manually fertilised (or any fertiliser added) for a few decades. I think it gets its nutrients from animals or insects, ants and things growing inside the pot.

mine lose leaves all the time..for me it is usually too much sun when i move them out into the catt area in the winter.