I have a watchman goby that has been in the tank for about 4 weeks and he seems to be doing fine, but about a week ago one side of his face and gill plate started turning white. I took him to the LFS and they said it wasn't a parasite, virus or bacteria. They suggested that it might have gotten stung by my bubble tip. He was out yesterday and I noticed that the other side of his face and gill plate are also starting to turn white. Does anyone have any idea what the problem could be?