Dendrobium Leaves Turning Yellow & Falling Off

[scy]

Hi Everyone,

I'm new to caring for plants and received 2 orchids as a gift about a month ago. I have a Cymbidium Insigne and a Dendrobium Hollywood. I do not have a problem with the cymbidium at the moment, just the dendrobium. Sorry in advance for the long post. I figure more details is better than not enough to save my orchid.

Problems:
1. The dendrobium's leaves are turning wrinkly, yellow and falling off a day or so later. As far as the leaf turning yellow, it's the whole leaf and not part of the leaf. (All other photos other than 1st & 2nd)
2. Has scale
3. Strange brown bump on rhizome. (Pic 2)

Growing Conditions:
I have my orchids behind a sheer curtain of an east facing window. The daytime temperature reaches anywhere from 72-75 degrees and night temperature of 60. For humidity, I set the pot on top of a tray full of pebbles with water (but I made sure the water level never touches the pot). I use a wooden stick to help me figure out how dry the medium is rather than sticking my finger in. (Pic 1 shows original pot & what it looked like originally.)

Actions Taken:
1. The original pot had poor drainage and was densely packed in sphagnum moss. I did not water it for nearly 2 weeks, because the moss was still very damp and wet. After I realized that the moss was too densely packed and it wasn't drying, I repotted it in a clear, plastic pot with plenty of side slits and drainage holes.
2. I also changed the medium to a medium bark mix. I soaked the mix in water overnight before potting it the next day. I also sterilized the pot and cutting shears with physan before beginning the repotting process.
3. I checked the roots and saw that they were thin. Some tips were black and gray, so I cut those parts out. After I was done trimming the roots, I soaked it in Physan for a few minutes to kill off any bacteria and repotted in the new pot. I repotted again a few days later, because the stem was very wobbly. I packed the bark more tightly.

A week later, the bottom leaf started to turn wrinkly and yellow. I've read that this could be due to lack of water, lack of nitrogen, or too much sunlight. I bought some fertilizer 20-14-13. The instructions said to use 1 tablespoon/gallon every 2-3 weeks. I read that "weakly weekly" was the best way to go, so I have been using 1/8 teaspoon per 1 liter of water.

When looking at the yellow leaf more closely, I noticed that there were small white spots that turned out to be scale. I used a cotton ball with rubbing alcohol to swab the leaves, stem and flowers and it left behind pinkish spots on the cotton. I immediately separated the two plants. I have been swabbing the plant once a week after watering.

A few days later, the bottom layer of green leaves turned yellow and the original yellow leaf fell off. Now the middle section of green leaves have turned yellow. I only have the 2 top leaves left that are green. The flowers are still beautiful and have not dropped.

I watered it again on Sunday and swabbed for scale. There was very minimal scale on the leaves and stem. I did find more of it closer to the flowers. Today, I saw an odd brown bump on the rhizome that was not there before.

Thank you for your help and advice!