Comet Fin Flicking Problems

[ConanTheLibraia]

My comet keeps flicking its fins, normally one at a time, like he is having a siesure or somthing. Also he keeps his dorsal fin down almost all the time. I have been giving him some melafix because another one of my fish died from ich. What could this be and how to treat it?

 

[heavenly]

IT is possible it is just a sign of temperature variations. It happened to my fish beofre. I hope it isn't anything very bad.