One of my White Clouds has something growing on its tail. I almost looks like its tail is falling off. She has started getting skinny and right where the tail starts it is a big white puff and then the tail is there. It looks like she is starting to have trouble swimming. I tried getting a pic but it is hard to get one because she wont stay still like the other fish do. I know its not Ich just looks like a cotton puff. Any ideas? I know its hard without the pics.. Im going to do a water change on the tank today and add some Melafix to see if that helps any.. But any ideas on what this may be?