Green Terrors grow very slowly after growing 3/4'' per month for a few months. As for Jack Dempseys, they aren't the fastest too, but they grow around 2/4'' to 1'' per month at MOST. They reach 8''-10'', although 12''-14'' has been seen rarely. Stop feeding live fish, or at least limit it to once a week at most. Just feed as you do, good pellets everyday, and try limiting the meat consumption to prevent deficiencies. If this were a carnivore, such as Clown Knife Fish, this would be something else. Try adding Blood Worms or Krill to their diet instead of live feeder fish. Feeder fish are known to help growth, but feeding a good protein food, like krill will help replace feeder fish, and at the same time, offer natural protein source and limiting the amount of diseases.
Also, start changing 50 gallons-70 gallons weekly instead, as the water quality can affect the growth.