Your situation could be due to these reasons:

1. The RTG needs time to get used to the new surrounding i.e to settle down. Ordinarily, most owners only feed the fish a couple of days after introducing it to a new tank.

2. With two other aros in the new tank, the RTG may be unfamiliar with their presence after having lived in isolation all these while.

3. Coupled with all the above, it is introduced with pellet food. Even under normal circumtances, the fish needs to be trained to accept pellet food. Chances are the RTG was fed with live prawns and crickets at the LFS. So, it requires time to accept the new food (probably a little more time than usual taking into account the other factors as well).

Good luck.