Yellowing leaves
 

I have a Dendrobium sp. in a vivarium and several of its leaves are getting yellow and some falling off. It is growing a new cane, but I am wondering why the leaes are turning yellow. It gets misted several times a day but is allowed to dry slightly during misting. The humidity ranges from 70's druing the day to probably 90's at night with temps in the 70's. Do I need to Fertalize this plant?

This orchid came from Lowes and I would also like to I.d. it. I will try and post a good pic when I get home.

Thanks

Ben