-Off topic
He's got the right tank size for it, but thats an ugly arowana. Looks underfed, barbels missing (well this happens sometimes can't blame the guy), head looks a bit weird too. You can say it's because it's old but I've seen old arowanas that retain a good muscular form.
I have a 22-24" arowana, tank is 300G. He's probably gonna stay there for life. The only problem I see with keeping them in tanks too small for them is a lot of them develop back/spine problems and get that ugly drooping tail. To each his own, I can't put a gun to your head and tell you to buy a big tank