while I agree with you puffer punk.. this in reality is rarely so due to tbh things outside our knowledge base even now in this hobby. owners should always strive to keep fish as large as their wild counter parts but rarely does it actually happen. even in Zoos.
tbh I think nothing smaller would be suitable for a fahaka then a 24" depth. ie a 120W min though prolly a 180. pretty new to puffers. but not new to challeneging FW oddball species. and of course bigger is always better. I wouldn't put a 14" Oscar in a 55... so I certaintly wouldn't put a puffer in anything smaller then it's potential max length. which seems to be about the 2' mark w/ fahakas.. and with as energetic as these guys are and as curiouse. You really can't go wrong with a bigger tank.
so.. a 90 would be fine for awhile indeed.. but def not for life.