I have 2 large tilapia that survived my first system 1 male and 1 female. I added about 30 smaller tilapia to my 300 gallon system. The new fish did well and grew out but I noticed a few missing. Recently I have found injured fish and several have died to what appears to be trauma. The large male often bullies the smaller fish and chases the female. Ive never seen them pull off a spawn. I also noticed the large male never eats any type of food I put in the tank. He's very anti social. I decided to separate the male and moved him to his own 20 gallon tank. I haven't seen any other fish losses and the remaining fish seem to be ok. They are a little shy from the stress of netting the large male. The large male won't eat now. Its been about 3 days since I moved him.
Well that sucks, BBQ time. Seriously though, he will not be able to go back to the main tank and give you different results. If he isn't eating what your feeding he is eating the smaller fish, survival of the fittest and all.
If you want to keep him I would get him some feeders from the store since he is refusing to eat pellets. If you don't want to maintain a separate tank you could sell/ give him away to someone as a pet or maybe someone has an AP system with other fish his size. It's a bummer but some fish are just more aggressive then others and it was a perfect storm in your tank with him having a very target rich environment.