Bronze Fan swimming head down

Question
Hi, i have a Bronze Fan, we've had him for approx 4 months, he was very fit and healthy, zooming around etc but I've noticed in the last week hes been swimming with his head down, hes been slow etc, and lies belly up for a while then when i check him to see if it is the end he'll swim away, not very fast though.His two little fins seem like they're just tired from all the wrong swimming that he just wants to lax out.Today i saw him stop moving his fins and shot straight to the top belly up.He is in a large enough tank and has a friend of another breed which the pet shop lady said they'l get along, hes fine. They have objects in the tank to hid in, changed water a few times and hes been fine.Same food, oxygen weed,filter etc.Do you have any idea what could be causing it? and how to overcome the problem.Poor wee thing, or does that breed like playing games? Thank you so much for your time in reading and answering this question.

Answer
Hello Mere!

It is a swim bladder disorder. Part birth defect, part too small a tank, and partly caused by deteriorating water quality. Up your water changes to make sure your tank is a clean as possible.

Feed him his normal diet, mixed with about 25% shelled and washed peas. Also, if you have a quarentine tank, it would be a good idea to give him some maracyn 1 and 2 for 2 or 3 weeks.

-Nick