Hi, I own 4 freshwater goldfish, three of them are fine however 1 seems to be unwell as it has been hanging at the bottom of the tank in the live plants for the past few days and its tail is starting to fray. It only comes up when I feed them but goes back down after being fed, it has also been breathing rapidly. I have added fin rot medication and have done a 50% water change yesterday but have seen no results.