Truthfully once your able to keep most delicate fish you'll see that it's all water quality.. Good that is... They can't be kept in small spaces with other fish,... As soon as they feel like they have competition for food the tank mate is history... This is from my own observations.. They eat crabs mostly. That I collect from the shore by the 100's... They will take krill in the beginning, but as they get older they tend to only eat crabs.. My octopus eat daily but if keeping more than one together... The key is to not let them know they have competition for food by offering regularly... This is very hard to do... This also means offering food 2 to 3 times a day after you get to know their patterns of coming out in the open... Mines tend to come out at 3:4oam something in the morning like clock work... Always start them off in a small tank to get them used to you feeding them, whatever you are feeding them...(krill,crabs, shrimp,lobster)..
But in short I just watched them a lot... I also talked to people that had them before actually purchasing them... Feel free to ask me any questions... Because I can't recommend any literature that pertained to the home aquarium.. But national geographic will teach a little...