Dendrobium problem

[VickiC]

Hello,
(photos included)
My Den has not looked healthy for a couple of weeks (maybe slightly less) and has seemed to look unhealthier basically ea. day-three or so. Fairly recently, I thought maybe it wasn't getting quite enough sun, so I moved it into a brighter area of my greenhouse gradually. Since it has looked wilty, I also kept a better check on the medium. I noticed small webs on it yesterday, as well as today. When I saw them, I thought "oh no...spider mites". I then checked the leaves, and there was absolutely no sign of the orangish-red 'powder' that would rub off onto my hand (as I understand it would). When I saw the web(s), yesterday I probably should have quarantined it from my other orchids, but I failed to. I don't know why I didn't....most likely because it was not near my other orchids. ?? Today, I did. I bought the Den a few months ago seemngly in good condition, and as I always do (whether necessary or not) I repotted it when I got home. When I unpotted it from the previous potting at the nursery, I found that the roots were fine, so I proceeded to rinse them and pot it into medium size bark and charcoal. Judging the moisture of the medium today (using a shish-ka-bob skewer), I'm guessing it's due to be watered again probably day after tomorrow (will be approx. 1 week). If it would help to know, the greenhouse airflow is very good. Ever so often, I notice small spiders (some are the little jumping kind), but I just haven't thought they were harmful to my orchids. I've never read anything about such spiders being harmly to orchids, and in fact, I thought they were probably an asset by keeping check on potential insects. Do you think it might be one of them making the webs? If so, that doesn't worry me, if you tell me that's not a problem. I thought maybe I didn't move the plant into more sun gradually enough, but I felt like I was doing it as slow as I should, so I assumed that sunburn wasn't the problem. ?? I would appreciate you experienced growers to be the judge, though. So, what do you think my problem is? I would really appreciate it if you will give me your advice.
Vicki
By the way, I realize my thoughts may be random and 'subject change' too much, but that's how my mind works sometimes.....not very organized. I apologize.