Which Congo puffer are you talking about Schoutedeni or miurus? As jib and homer said miurus is a fish eater. While Schoutedeni eats a wider variety of stuff mostly insect larva, small insects, water bound inverts such as shrimp and snails. I have heard of people getting Schoutedeni to eat pellets especially vibra bites. I tried vibra bite with mine and she was so disgusted by them she wont even eat bloodworms anymore. I tricked her into trying the bites by putting in bloodworms at the same time she grabbed a bite chewed it for a second spit it out, tried it a second time and spit it out again. Ive tried it a few times since then and unless I feed snails after she wont eat anything else I put in her tank that day. As soon as she sees its vibra bites she sulks at the bottom of the tank in the corner. She will eat brine, mysis, krill, market shrimp, and she absolutely loves bladder snails.