Puffers are tough, being scaleless they become barometers for any water parameter issues other fish ignore. Cichlids are fairly dirty in general, so I imagine the water was not to its liking. We have a 14" Fahaka in a 150 gallon and do 75% WC twice a week with a 2262 and 2217 on it. If the Nitrates creep beyond 30 she notices and starts skulking. Great personalities and we adore her, but certainly a difficult fish. Think about an upgrade to its tank (30-55 gallon), overfilter, excessive water changes, and have fun they are certainly cute fun fish.
"In the land of the blind, the one-eyed man is king" Desiderius Erasmus