A girl in Boston trying to grow delicious food on a balcony and some sunny windowsills. And now with a gro-light too.
I have very minimal experience with orchids..have only one. They don't like a lot of water I read..just once a week and an orchid fertilizer as per directions. However, if you go to Jodi De Long's blog, I am sure you will find further info. http://bloomingwriter.blogspot.com/2011/01/garden-of-indoorsphalaenopsis-orchids.html
I've personally worked with hundreds of orchids and there doesn't seem to be any rhyme or reason to when leaf yellowing occurs. It seems to happen over night and without any cause. I would just cut the leaf off and move on.