An octopus has way much more needs in filtration than any fish on the same size. Mainly for me it depend on your biological and chemical filtration as also the ability to be able to close the tank "smart" because of the fantastic escaping abilities of these great animals.
I also think that 10g might be too little, but i guess it depends on the species size you have decided to keep.
As far for biology, since an octopus is a really heavy eater, you will definitely need external biological filtration and a big pile of carbon is a necessity in case the animal feel scared and release its ink.
It's not a simple animal for aquarium, but hell is beautiful!!