Whats wrong with my Sturgeon ??

[fishbreeder12]

My Diamond Sturgeon just swims around in a lack-luster fashion. He is oriented nose pointing up. He sits at the bottom a little ,just mostly swims like this.

He's about 4-5 inches long. His tanks mates are two koi ,two goldfish ,3 mahseers ,a pleco ,and a sterlet sturgeon. THe other sturgeon is doing perfect.

http://youtu.be/oORHytyiphE

 

[AU_Arowana-RG]

Maybe it has to do with the water-quality. How often do you do water changes?