I think the problem is lack of ventilation and maybe overwatering. The pot you used for decorational purposes might be to tight around the clear platic pot.
If you use an pot for decoration, make sure it's larger than the pot that holds the orchids, let's say at least 1/3 of an inch wider.
Sounds like your orchid has been too wet too... (I think what you've seen on the pot is mold). Maybe you can put some clay pebles on the bottom of your decorational pot, but keep this dry! The clay pebles help the are flow beneath the clear plastic pot.
Just my 2
Nicole