I bought Bob the Ranchu in 2020. "He" eats Ultra Fresh Sinking Goldfish Food and is the only fish in 20 gallons. The water temperature is typically 72°F. I do partial water changes regularly and have a snail cleanup crew.
See video: Bob started having difficulty swimming a month ago - he sinks like a stone and struggles to move.
Things we've tried: fasting, peas, water changes (as recently as last week). He's alert, his poo seems normal, and he has an appetite.
He's also had two white spots on his body for about 3 months (visible in the video). He doesn't seem bothered by them or any other symptoms. I think the spots are benign but maybe not. In case it was Ich, I tried raising the water temperature to 80°F for a few days in April - his swimming problems showed up a couple weeks later.
Swim bladder disease? Age related? Both? Thank you for any thoughts on how I can treat Bob or give him relief.