jesus who did you get em from? did you use bacteria bubbles to get the filter system up and going? normally you have 2 have the tank up and going for a few weeks before going to fish like them. i use a small specialist shop because its their livelyhood. big places like seapets etc just have people who just want to be paid and dont care.
puffer wont touch flake. i use a mix of frozen food and flake. i only feed every 2 days. gourami and knife fish are very soft fish and susseptable to getting ill unless perfect ewater conditions. keep an eye on em m8