I'm posting this for my grandparents since my grandfather has been stubborn and not really willing to treat his fish, my grandmother though has started asking for my advice since I keep fish. They have 1 comet and 2 regular fancy goldfish in a 55. I believe they feed omega one and spectrum community pellets. They're all several years old but one in particular (one of the fancies) has extreme trouble swimming. She (don't actually know but they call it she) sits on one side and swims short distances for food but generally doesn't swim from one corner and just sits on the bottom. I can try and get my grandmother to send me pictures of her, but she's apparently been like this off and on for 2+ years. I suggested maybe parasites or bloat and told them to only use pellets instead of flakes and I bring their fish f/t bloodworms and peas when I visit. I know this is very vague and I apologize because these aren't my fish but in the next few days when I see my grandmother I can try and get some more info.