Something Wrong

[somethingfishy]

I have a ten gallon aquarium with three rasboras (harlequin), an algae eater, and two female bettas. They have lived together happily for quite some time. Yesterday, however, I noticed that one my betta girls had black stuff on her tail. It isn't fungus i dont think, it is just some black things in the middle of her tail. My other betta doesn't have anything wrong with her at all. I just wanted to make sure that it isn't serious.
Thanks

 

[WILDER]

Just add some melafix or salt to see if that helps.