I had a similar problem with one of my own glass catfish and posted a thread a while ago, with pictures, does it look like what's on mine? I didn't think it was ich either but I took it to my LFS and they told me it was.
http://www.aquariacentral.com/forums/showthread.php?t=108880&highlight=phantom+glass+catfish
http://www.aquariacentral.com/forums/showthread.php?t=108880&highlight=phantom+glass+catfish