The fish is a baby and it is stressed out due to the lack of hiding places in the tank. The tank is also white and glary and that isn't good for any fish. When algae starts to grow on the rock it won't be as bad, but the fish will be stressed for a while.
If you add some plastic or live plants (Caulerpa or Halimeda), that might help. Reducing the light intensity might help too, but that will slow the growth of algae.
As for the feeding,
@Donya covered it. Very few species of marine fish tank food from the surface in the ocean and even captive bred marine fishes don't take floating food that readily. It is not natural for them to take food from the surface. If the fish have been fed on frozen or live foods, that will also reduce the chance of it taking food from the surface.
Getting a second anemone fish might help but make sure it is smaller than the current one.
