thanks all
I had the camera pre-focused and on a tripod with a remote flash through a small umbrella just behind and to the side of the camera. Held the cable release in one hand and shrimp in the other over the spot I was focused on. To focus, I just held my hand out, focused and took a test shot.
He goes crazy when he sees me walk toward the tank, when he was about 3 inches long he started grabbing the food before it hit the water.