Corals don't like direct flow, they like random flow, which is best achieved by having 2 powerheads on opposite sides of the tank pointed towards each other, so the flow bounces and creates random pattern in the water.
What are your water parameters? What kind of lighting? When did you set up your aquarium? How long have you had it?
Nice some real questions so the light is an aqua night newer one so it has a timer n all and the rest you could veiw on my only other post if you could