Depends on where the octopus you get comes from, and so it's important to research what species you plan to keep. Bimacs should be kept in cooler temperatures, 72 or preferably a few degrees lower. Caribbean species are fine at your typical mid 70's.
Common brown pacific can be any species from the Pacific ocean. You will be fine keeping it at 76-78 until you get a positive ID. There are only a couple species common to the trade that enjoy colder water.
Yup, that description doesn't mean anything as far as species goes, but at least you know it's from the Pacific. Make sure it's not a Bimac (California coast-Pacific) I think 76-78 would be a little hard on it. California waters stay fairly chilly year round.
Hey Everyone, my LFS called and my octopus is coming in this friday at 10 am at his store, and he said it is a common brown atlantic octopus, so what should i set my temperature too if its atlantic, it is at 75.5 F right now.