Not trying to rain on your parade man, but I would just get rid of the BGK too and get smaller fish for the 55. You bought the BGK and the arowana before you knew better, now you are learning. There is a learning curve for sure, and you're on the right side of it. When I was young I kept a giant goldfish, probably 10", in a 20 gallon for years. Because I didn't know any better. Once I became more interested in the hobby and started doing research, I found someone with a pond for the goldfish. And kept smaller fish in the 20. Which I enjoyed much more because I knew it was a good home for them.