I've been having a problem for a while which is two of my four fancy goldfish are overly aggressive. Right now I have my 55gal tank separated into three sections with nets. I hate how it makes my tank look but I can't leave all four together because I worry for their safety. One of the two causing trouble is Nick, a black moor. He use to torment all of my fish until I separated them. About a month later my pearl scale started to do the same thing to my other two, Jimmy (an oranda) and Callisto (a demikin), and they were battered. After they were separated for about a month I tried to re-introduce them together, but nothing had changed. I was hoping someone had a better solution than just separating them. I don't want to have to get rid of Nick or Toby but I feel bad for all of them because they don't have as much room as I wish they did to swim . Thank you for your time.
(P.S. - I have monitored all the levels of the tank and none of them show any problem. Also I have had all of my fish over a year, and they have been separated for about a month, Nick about two. All but Callisto are male)