Dendrobium - leaves turning black
I picked up this Dendrobium 'Elma White' off the clearance rack last year. After a few months leaves started getting yellow and then black ... starting usually at the tip then eventually (fairly quickly) turning completely black (this was a while ago, so not sure of the exact sequence). I switched out the moss substrate that seemed over-compacted and was burying the lower few inches of the stems. It ended up losing all the leaves, but i left it and lo-and-behold, new growth started! However, now one of the new leaves has turned black also and i'm seeing some black spots on another new leaf. Is this a disease or maybe something as simple as overwatering? I've looked at several sites and can't seem to find a description (or photo) that seems to match what i've got going on exactly. Any ideas from the experts out there?