Well, to be quite frank with u, most octopi are perfectly fine in a 29 gallon, sometimes in even smaller tanks. There are smaller species that you could buy, but it would have to be by itself. The eel would definitely eat it. Its really hard to pair up octpus in a tank setup, and it would have to be a species only becuse watever is in there it will either eat, or be eaten. It will eat smaller fish, or be eaten by those larger than it.