I have a 11" red tail golden arowana, 4" phoenix and 3-3" silver dollars, currently in a 100gallon tank but not sure what should be the next size and when?
I wouldn't go ant narrower than 30" with that Arowana. I had a Saratoga once that had to do a sort of front flip out of the tank to turn around in a 6X2X2 he was eventually relocated to a local Aquarium.