Ember Tetra Nipping Betta! :(

[CrazyDiamond88]

A few days ago I put my betta and 6 newly bought ember tetras into their 12 gallon tank.
 
All was well except just now after I fed them, I was watching them, and one of the tetras was following Kasai, my betta around, and nipping his tail

Kasai seemed pretty flustered and flashed himself away.
 
This tetra is persistent though, he keeps going after poor Kasai who seems a little bit harassed.
 
What should I do? Am I worrying too much? Will the tetras have to go?

 
Edit: I suppose, if need be, I could take them back and get some pygmy cory cats instead...

 

[CrazyDiamond88]

I was just watching them some more, and the bratty tetra was nipping and following Kasai again. 
Kasai turned and flared at him for like .5 of a second then swam off.

 

[CrazyDiamond88]

I guess I could just take the nippy guy back and get another? 
I was planning on getting another 2 more to make it 8, as apparently that can also help with nippiness? 
 
Sorry for posting so much... I am so worried :c

 

[Shelster]

Tbh I would exchange for the cories, but failing that try upping your embers? Thing is, the others also may start to nip the poor guy

 

[CrazyDiamond88]

Yeah, I am so caught about what to do
 
Would it be good to go exchange Charlie the nipper for a more placid tetra, and then get another two to make 8?

 

[Shelster]

You could try, but what's to say when the others 'find their fins " that they won't do the same?

 

[rpgmomma8404]

I'd go with the cory cats. They are fun to watch and I don't think you have to worry about them going after your betta. 

 

[CrazyDiamond88]

D: really? So I should just give up on the tetras?
Eh. Ok.

Will the cats rip up my plant carpet? It's not very well established at the moment.
I can go change the fish this weekend I suppose.
Kasai will feel better. Poor thing is being harassed all the time

 

[Shelster]

Not at all, mine never bothered my plants -the pygmys are lovely, won't even notice your betta either.

 

[CrazyDiamond88]

Yeah I will have to do the swap.

I've now noticed he has two tiny holes in his fin
Not sure if that's from Charlie or from snagging it somewhere

 

[TallTree01]

With clean water it should heal up in a few days to months.

I agree with the cories btw.

 

[CrazyDiamond88]

Oh god. Came home today and found Charlie floating dead at the top of the tank.
 
His eyes had been picked out and part of his tail had been picked off too.
 
I am pretty sure Kasai just snapped and attacked him. 
 
I am going to move Kasai into his old tank till tomorrow when I can return the tetras.
 
I'm really shaken by this first fish death I've had.

 

[TallTree01]

Sorry for your loss diamond.

 

[CrazyDiamond88]

Thanks tall tree. I feel pretty bad that I didn't do more to prevent this from happening
I should have moved kasai yesterday. I thought it would be ok.

Do you think it was definitely that kasai killed him?
The other fish are all perfectly healthy so I don't think there is disease.