I've had my betta fish for two years now, he's lived happily in a glass fish bowl. He is very active and only recently has started to slow down. I found him the other day with stringy white film coming off him and I was sure he was dying, researched cotton wool disease.. Changed his water and added some salt.. The film disappears but his long trailing fin has rotted off!! Is there anything more I can do for him, or is this the end? He is still swimming around and eating, but he doesn't look too good.