Fancy Goldfish being abnormally aggressive
Around 4 days ago, I bought 2 small orandas to be friends with, at the time, my lonely oranda. I own a 45g tank. The day after the first day, the one I named bronze medallion started nipping at my original oranda, which I named Diamond, because at the time I assumed it was because he (Diamond) had the biggest fins. I decided to just wait it out to see if the behavior would stop. Big mistake. A day later both Bronze Medallion and the one I named Creamsicle which was the other new oranda, started nipping at Diamond. All parts of Diamond, not just the fins. Especially his anus. Days later Diamond is unable to swim because of malnutrition and stress and dies. (RIP Diamond, you will be missed). Now Bronze is nipping at my other fish (Zebra Danios) to the point one of the six of them is actively bleeding and has a fungal infection. Is this normal? What should I do?