I think this is my favorite. They are typically classified as nocturnal or crepuscular (early evening, early morning hunters) but are seen even in the wild at all times of the day. They do need a large aquarium, typically 130+ gallons. They vary considerably in size though, you just can't count on one being on the smaller side). We have one being journaled as we speak. Check out Casper's thread.
Good choice in avoiding the mimic (almost guaranteed not to be Thaumoctopus mimicus and more likely Wunderpus photogenicus but at least one other species has be labeled mimic), not only do we not know enough about their current numbers in the wild, they do not do well in captivity. Here is a group of posts I gathered to help new keepers understand a bit about (lack of) species selection most often found for home aquariums and what to expect when you keep an octopus. Please read all of the Box of Chocolates post (include the intro before reading on about the different species traits).
A 70 is a great size (hopefully with sump) for most of the animals available to us. I have raised a vulgaris in a 62 but was lucky she remained small for the species. I did have a 140 well cycled and available if she out grew the tank but octo-proofing it would have been a major challenge. Each animal is different but the medium sized animals we keep will usually adapt to a regular feeding time even if they are primarily nocturnal. All that I have kept from very young stay mostly hidden until sexual maturity (about 5 months of age).
Awesome, I think I'll start the O vulgaris in the 70 gal. And eventually upgrade to a 150 gal. I love the looks of the mimic octopus, but I've read about it and they're very few seen in the wild. Thanks for all the information.
Do read my notes on obtaining an octopus in the referenced Box of Chocolates notes regarding hoping to find a specific species. These are not mainstream animals and our vendors rarely know what they have for sale. It is very important to internalize this concept as you "can't send it back". The good news is,whatever species you end up with will likely be enjoyed.
Just for confirmation of my doubt or my error, ask where the animal will come from. Actually being able to order and receive a vulgaris from an LSF has not happened in the 10 years I have been on the forum. Almost all inland pet stores order from wholesalers and almost all octopuses from wholesalers come from Indonesia (mostly the Philippines - this is clearly the case of the vendor who offered a "mimic"). The most "common" octopus from the Philippines is an animal in the Abdopus family, often aculeatus (sometimes labeled "common" brown octopus). Of the few that come from US waters, the "common" octopus is O. briareus (the Common Caribbean Octopus) or the "common" dwarf, O. mercatoris. At one time we could occasionally get a vulgaris from the Gulf through live rock farmers (but this was rare and not been the case for almost as long as I have been a member). I do know O. vulgaris resides along the US Atlantic coast and is not particularly uncommon because of a PhD study currently monitoring their shared habitat with Macrotritopus defilippi (Atlantic long arm). The vulgaris we have seen on TONMO have almost always been mislabeled or one offs hand caught (or collected as crab/lobster bycatch) and sold by Florida fish collectors.
Please don't take my posts as argumentative as they are meant to be informative and prepare you for your adventure, not discourage you from having it.