at the size this one is a 3 footer will hold him for a while (6 months)
bigger ones are a real problem
they like to dig under things and are incredibly powerful, collapsing stacked rocks, digging up U.G. filters etc
they can push lids off tanks, so some heavy weights are needed
i think from memory a 3 foot octopus can manipulate himself through a 3 or 4 inch hole
an octopus is very intelligent and can suffer depression in a fish tank and just give up and die, that is why the younger you can get them the better they settle to tank life