Welcome to Tonmo!!! Sure, a 30 can house many types of dwarf octos...the only trouble is, no one is captive breeding them at the moment, so you have them for brief periods...a 55 can hold a bimac for its lifespan, that is why we push that size tank so hard...do you already have a 30?
Glad you found us,
Unfortunately, no. There are no(at least that I know of) non-dwarf octos that can go in a 30g. I know, I've looked! (I have one) Jim at octopets might be getting aquacultured Rossia pacifica and Sepia bandensis soon, though. (still waiting for a reply email from him)
I have found a fifty gallon to be a good size for an octo tank from the standpoint of maintenance (provided you don't have a bimac who grows extra large, like mine did- could have used a bigger tank, but we made do!).
A ten percent water change is one of the five gallon jugs that the LFS sells, and this quantity of water fits nicely into the big empty 7 gallon salt buckets. It's about the limit of what I can carry around. A larger tank, and I'd be using more jugs of water, more salt buckets, etc. Taking care of my 19 gallon invertebrate tank seems to be almost as much work.