I do not think he is likely spiting out the squid as much as he may be having difficulty eating this more chewy food. Also, even if he may not be loving it and spiting some out, it often takes puffers a bit of time to get used to a food they are not used to eating. Keep offering it. You just cannot feed the krill as a main food. I know he loves it because all puffers love krill. People often jokingly refer to krill as "puffer crack". The problem is if he relies too much on krill as a food source he will develop lock jaw and die. You can continue to feed a single type of meat and switch them around each day. If you go this route, I would not feed krill more than twice per week. I think, however, it is much better to offer a group of different meats every day at the same time. I think also by offering the variety of meats at the same time you will be able to condition the puffer to like other foods more quickly because the foods he may not love will be fed at the same time as the food he loves, thereby helping him develop a more favorable association with the foods he may not love.