after reading the thread for a while, i wonder if the explosive growth of the gar is due to appropriate tank for a SMALL gar ... imo a small fish in a smallish aquarium with no competition for food will have an easier time finding food.
IME when my gar was puny it was in a 6' aquarium with a separator so he had no trouble finding food ... as he grew, i varied food (eels, fish, frogs) and he ate and ate and ate - and grew and grew and grew - until i moved him into 3x2m aquarium ... the growth has slowed down considerably after 2' BTW he is ~3' now after two years (from 4" baby).
Eating habits also changed drastically when moved to a bigger set-up: no chasing of food (e.g. fast moving fishes, eels), accept floating pellets (gourge on that), still eat frogs and prawns. Not growing as noticeably though. Also, the competition for food in the large set-up is also much fiercer: another two smaller gars, 2 RTCs, and now 3 juvi paimas. I had to change feeding pattern to ensure there was food that paimas do not accept (e.g. large frogs)!!!
finally, my biggest gar was never a killer - the only casualty is a silver aro which he killed in his earlier life (went through a divider to murder the poor fella) ... i supose a platinum koi does not count .... he tend to not like silvery fishes ... e.g. dark oscar is fine