How can I stop my black skirt tetras from fighting?

Question

I bought 2 black skirt tetras along with some other fish for my 10 gallon tank. The next morning one of the tetras died, from stress I think. The other tetra was on its own for about 5-6 hours, then I added another black skirt tetra into the tank. Now the old one keeps trying to nibble at the new one's fins. He tore a piece off and every time the new one starts swimming around, he gets chased by the old one. And now I'm noticing he's started to nip at my other fish' fins.

What is the cause of this? How do I stop it? If I take the bully fish out and put him in a different tank for a week or two and put him back in the 10 gallon tank, will it make him less aggressive?

I'm scared the new one will die soon, which is sad.

Answer 1

The answer is pretty simple: buy more tetras.

Tetras like to live in shoal. I would say something around 12 for your tank size.

They will get more calm with more fish because they will lose territory(I don't know the exactly theory, but I had many tetras and they were fine in shoal).

Also it will look beautiful because they will swim together. They have a kind of hierarchy, so the strong ones will be at front of the group.

Answer 2

I do know that if the fish is bigger then the rest of the fish in a fish tank, I have had experience of aggressive fish in a aquarium, you can add more, but there is a risk of over populating, but you can create an area of smooth driftwood, plants so the tetra can hide in.