i'm just wondering how big they get because mine will be here tommorow!

www.cephbase.org still lists them as Octopus filosus, and according to cephbase "body to 7cm, arms to 30cm"

That's about 2.5 inch mantle and 12 inch arms. That must be arm tip to arm tip, as the ones we have kept have all had relatively short legs.

what is minimum tank size?

Questions you should have asked maybe before you got your new octopus? :)

50 gallons should do fine. They like to roam a lot.

it's going to be in a 75 gallon but i'm just making sure because this is my first octo and i want it to be as happy as possible!