if he is acting normal and seems to be fine i would not concern myself. He may be scavenging when your not looking.
I would start to worry when you are seeing physical signs of malnutrition like him getting skinnier actling lethargic and just not as active.
He still may be getting used to his new home.
When you go up to the tank does he go and hide or does he act frightened or skittish??? It should be a very easy acclimation with him being the only fish in the tank.