Fish anus infected?

[joshik]

well ive been QTing my new anthias for a few days now. i noticed the smaller one of the two is constantly moving its tail really fast and when he stops, he shoots up... so im thinking he has a swim bladder problem. .... also, when looking carefully at him, his anus area is kinda black...looks infected.

any suggestions or ideas how to help the little guy out?

 

[bullitr]

Try melafix
It might be a fins rot
Picture helps