IMO the butti is gona continue to grow incredibly fast and continue to limit your tank space by forcing you to use the divider. I've owned them, many of us have owned them, they're big and MEAN. You probably don't want to hear this but I think your decision making leaves a lot to be desired. 3 of the 4 fish you have in that 55 will end up over a foot long, and by the sound of it they're already tearing eachother up
Buying the first three and putting them in there wasn't a good idea IMO, but then you added a DOVII??? WTF?
sell all the fish and buy a turtle