I have a flat head. He is very to himself. I bought from a guy who said he had never seen him eat but he was growing. I have him in a 800g pond and he is never out in the open. I rarely see him. I turn out the light and feed him sinking pellets.
Ive got a red light I've used, I don't know that the Flathead sees it, but the other fish seem to notice it and stay out of the brighter areas. I rarely use it at all because my flathead likes the bright light anyway.