I've "quarantined" the pleco to prevent my other fish from nipping at his wounds. Yes it did look like a cottony mass. I added a little melafix to my "quarantine tank" which is a 1g bucket, air pump/bubble stone, and a heat lamp.
Do you think its safe to leave him in my actual tank?
Also the part about him hiding...well he doesn't really hide. As a matter of fact he seems to be really sluggish and lazy...ALL THE TIME. He's acted this way since I brought him home from the LFS