I'm sorry...did you say you bought this fish at an ace hardware? lol.
In my honest opinion you'll need a 4 ft wide tank and at least 7 feet long...aros swim ALOT and can easily hit 2.5 feet in an aquarium setting with good care.
Yes I did lol, my local ACE carries a better selection of healty fish than I can find for at least 3 hours any direction, including south american stingrays and peacock bass. The largest tank they carry is a 220 with a stand for $1,100 so that's why we were planning on using that in a year to move the Arowana into, as ACE has another Silver approximately 3 feet long in a 220. I agree bigger is better and I would like to build a tank into a wall in my basement with dimensions of at least 10'x6'x5' but that is a ways in the future. If I can manage to fit a tank larger than 220 down my basement stairs I'll get that instead of the 220, but until I can build my own I want a good sized tank for probably the first 3 years of an Aros life.