A 10 gallon is really pushing it. The problem is that octopuses produce much more waste than a similar sized fish, causing the water conditions to deteriorate quickly. In a tank that small, disasters can occur very quickly. If you were to upgrade to a 20 or 25 gallon with very good filtration you could keep an
Octopus mercatoris. They are very small octopuses and quite common in the trade right now. The only downside is that they have a deep-seeded nocturnal lifestyle so you would have to stay up late at night to enjoy them. Many of the larger nocturnal octopuses tend to adapt to daylight hours, but I don't think anyone has had any luck getting a
mercatoris to do such. On the other hand, their offspring can be raised relatively easily if provided with enough live food and a member here has had luck raising a second generation and some of them have lived over a year, in small communities which is uncommon among other octopus species.
To really get the most out of the experience of owning an octopus, you should consider a 50 gallon or larger and one of the commonly available mid-sized species. They are more outgoing and are much more likely to become interactive and display the behaviors that draw interested people to them in the first place.
As for general information, there is a lot of great information in the ARTICLES section of this website.
TONMO Cephalopod Community
Before you seriously consider getting an octopus, take into consideration that none of them are likely to live more than a year and dwarf species generally have an even shorter lifespan. On occasion people can keep them up to 2 years. Honestly it's a gamble when you buy one because more often than not the ones available are mature adults with only months or even just weeks to live.
If you are familiar with keeping a saltwater tank and have successfully kept corals, then keeping an octopus shouldn't be too difficult so long as precautions are taken to seal the top of the tank and all of the filtration and powerheads. They are very curious and keen on squeezing through the tiniest of spaces which can lead them to serious injury or death by escaping the tank or getting arms caught in pumps. They definitely fit into the advanced care category.
You have to plan ahead for the expense of paying for live food. Sometimes they will accept dead raw items, but more than likely they will have to be trained to accept those items so plan on keeping live crabs, snails, etc. You don't want to use any freshwater items.
Copper kills octopuses, so used tanks or tanks previously set up as freshwater displays can be risky.
I think that's about it as far as the basics go. Welcome to TONMO.