My friend has a gold fish and being the fish lover that I am when I go to her house I like to sit and stair at it, well today I noticed that his tail is no longer there and I was wondering what if anything could help get rid of this and grow his tail back. I told her to do a water change to get clean water in there and to go to the pet store, but it would be nice to tell her what to look for at the pet store to fix this problem.