When they are first introduced to an aquarium we have seen octopuses exhibit either gluttonous consumption or stubborn refusal. I recommend continuing to offer food every day and remove anything not eaten after a couple of hours. Initially, size seems to be important and I have found that starting with small pieces (about the size of the eye) seems to work better than offering a single large portion. Once the food is accepted and eaten, I increase the size until there are left overs. Quantity consumed will change over the life of the animal with young animals eating more as they grow into adults and older octos slowly consuming less. It also seems best to develop a diversity of accepted food and alternate during the week as the larger (ie not dwarf) octos I have kept appear to get "bored" of the same food every day.