We're almost certain that a sharp pH drop caused by our chaca killed our congo puffer so now we monitor the pH in his tank very closely, daily in fact.
Our Chaca shares his tank with two (jellybean?) parrot cichlids and a purple spotted gudgeon, all of which are at least twice as big as the Chaca.
After a lot of effort, we moved him from eating live tetras to gut-loaded live river-shrimp and now he easily takes peeled prawns and whitebait with no trouble at all.
Because he's so lazy and will starve himself rather than actually look for food, we have to feed him by hand using snake tongs. We feed him every third day.
he spends 99.9% of the time buried up to the eyeballs in the sand and does absolutely nothing except sometimes at night we hear him croaking.