tetra acting funny

[fishing]

I have had a school of serpae tetras for a year and three months now. One of them is acting funny. He is constantly swimming up to keep his balance, but keeps sinking to the bottom. No probs with the other fish. What is the problem with him?

 

[Menagerie]

He made have a swim bladder disorder. How are the water parameters (ammonia, nitrite, nitrate, pH)? Of course, he also may be nearing the end of his life span (I'm not sure how long they can live).