jackb
Garden Master
It appears cat may be right about the overwatering. After a period of time, the media breaks down and no longer drains, and more importantly air can not get to the roots because there is no texture in the media. It just becomes almost like muck. The top may look fine but the interior becomes a sponge and retains water and prevents the roots from breathing. The roots need air and after you water them they swell but need to dry quickly. They retain water for quite some time and can tolerate being dry for a while. If you run the plant under a faucet water should flow freely through the container. Examine the roots and if the media around the roots is more like potting soil than orchid mix that may be your problem. I prefer a mix of four parts clean fir bark to one part each of charcoal and perlite. Commercial mixes are OK in a pinch, but make sure you rinse the mix before repotting the plant. I have over a hundred plants and water them only when they are dry. After a while, you can tell just by lifting the plant if it needs water. Also, you can gauge the health of the plant by looking at the roots; white roots with little green tips equals a healthy plant. If you look closely at the photo you can just see a little bit of green on the tip of root before it heads back under the media.
The photo below shows what the media should look like.
The photo below shows what the media should look like.