I have had the same problem a bigger tank is needed. I had 75 gal with a P. Congicus and a Ornate and edlicherii. all 6,8,10 inches they all nip and fight now I am in the middle of the best poly tank 2 of them one for smaller bichirs and one for the larger ones . the larger one is done my poly are all over 15 inches now they are in atank 130x36x18 365 gal not a problem . and I just added a 14 in lapradii.