Welcome to the forum!
Krill has been associated with lockjaw in puffers, so I’d be hesitant to feed that to them.
As for pellets, good luck but it’s unlikely you’ll get them to eat them. Most Puffers are notorious for not touching anything but live/frozen foods (with the occasional freeze dried), and amazons are some of the worst when it comes to that.
Mine loved frozen mysis shrimp, and tubifex worms would be good as well.
I’d also look into blackworms and freshwater amphipods (scuds) for live foods.
I personally haven’t, but many feed clams on the half shell to puffers.
Lastly, I’d try breeding neocardina (cherry) shrimps for them to eat.
Picking smaller live foods like scuds off rocks will help keep the beaks filed down.
Given the rate at which the beaks grow and the highly active nature of the fish, my theory is that they have a much higher metabolism than most puffers and therefore need much more food to grow and thrive.
