In the spring, a friend tipped me off that a Japanese/Korean restaurant in the GTA (Greater Toronto Area) was selling live octopus. I keep a number of saltwater aquariums, including a 15 gallon tank hooked to a chiller in the basement and decided I would try one. On July 25, 2017 me and my 6 year old daughter purchased one, looking into the restaurant aquarium that was packed with live octopus, most looking in decent shape, we picked the one seemed to be trying to "follow my daughter" almost like it was saying "pick me", maybe it was her bright red hello kitty shirt! When we got to the car we put it in the small plastic aquarium we brought, inside a cooler box with a couple ice packs and headed home, a two and a half hour drive. Upon arriving home we place it into the aquarium with the temperature set at 60 F with a 4 degree variance (60 - 64). The following day Sushi wasn't looking to great, and on the second day he was even worse, here is a video of Sushi on the third day, as you can see he was pretty sad looking, barely responded even when touched, breathing very heavily. I tried feeding him a shrimp tail but he showed no interest at all.
Knowing he likely didn't have long to live I decided to try lowering the water temprature, I dropped it to 55 F with a two degree variance (55-57), the following day I checked on him, almost expecting to find him dead, instead I was amazed to see arms actively moving all over the place, his color was alot better and he was MUCH more alert. It was amazing how much he improved in just 8 hours! Two days later I offered him another shrimp tail, this time he eagerly accepted it, eating about a quarter of it. Ten days later I shot this video, as you can see he is alot better.
Its now well over a month and Sushi is doing great, I feed him a shrimp tail every week, we normally eats about a quarter to half. From my own experience I truly believe these "Korean octopus" are a cold water species. I know others are also keeping "Korean octopus" from markets and restaurants and hope this helps.