Someone with more time and knowledge will probably come by and give you more details, but basically, octopus should be kept in their own tank, they will eat fish and inverts. Water quality must be kept very good. Also, the tank needs to be modified so there are no holes the octopus can squeeze through and escape. They have a beak for a mouth and if the beak can fit through the hole, the whole octupus can fit through. (This means a 6 inch octupus could easily sqeeze through a 1/2 inch hole). They will eat shrimp, also mollusks are good. Crabs are usually a favorite. Also, even if the octopus is kept very healthy, it still has a short life span, I believe around a year.