I have a platy (one just like the one in my picture) who this morning started acting really bad. Poopy (his name) seems really boyant and isn't using one of his fins as much as the other one. It takes a lot of energy for him to swim downwards. I also noticed that he seems to be bent in the middle. I went to class and came back and he was stuck to the filter.

I have just taken him out and placed him in a bowl of his own using water from the tank. I figure we just have to wait and see... but are there any suggestions?
Side note: 4 days ago I added the 2 Balloon Molly's to the tank. They don't seem aggressive but maybe one of them attacked Poopy??