Hi! Not sure if you received any help for this? Is it still a problem? When I had fish that would bully others, I always tried to physically separate them, especially during feedings. Can you isolate the bully tetra by placing a plastic separator (can be a flat perforated sheet stuck in the gravel or held up in the tank decorations, up all the way to the top) between it and the other fish? Of course only during feeding time :)

tetras like to school, maybe a couple more for the tank?