Ohh boy... another rouge Tiger Barb! I know just what you are going through...
I had my bad boy TB... he was the devil himself. didnt matter what tank I put him in and who was with him.. he just went after everyone and any species!
There was no changing him til he had to live by himself then he had no choice but to behave. When a friend who had very large TBs for years volunteered to take him off my back I was thrilled! Sometimes they are just evil.. pure and simple lol...
Best of luck with the lil...well, I cant swear, but you get my drift heheeh...
I'd say bring him back to the LFS, he may not give any of your other fish peace.
