When I feed my betta in a toplighted tank, it doesn't work. If the light is really bright, it seems like it blinds him. I have to turn off the top light, and turn on surrounding lights so he can see me, and the food when I drop it in. I've conditioned him to recognize tapping on the top of the tank as feeding time too, though. I'd just suggest trying the feeding with the top light off and see if he can actually see it, first.