whitecloud minnow

So, I'll try and keep this story short. The picture above is my sister's tank. She's 13. Her bf is 14. Here's the thing. His parents are very wealthy, and they adore my sister, but they buy her whatever she asks for. When she was 11, she wanted goldfish, so I got her two, but I knew they'd...

My whitecloud had his front fin bit by the other whitecloud in the tank and he is now swimming weird. He only uses the opposite fin and wiggles instead of swimming. He also starts to float upwards if he is still for a period of time. Any treatment/medication recommendations?