Here are some settings for these photos.
Full tank shots - 1/20, f8.0 ISO 400
Fish - 1/50 to 1/80, f5 to f8, ISO 400 to 800
Corals - .5 sec., f11 ISO 100
Moving corals (hammer) - 1/40, f10, ISO 400 (pumps off)
I use shutter priority. I set the speed and the camera set the aperture.
jccash I am not sure why your pic is so small, It seems that you have a white balance issue. Your pic looks too blue. Try to preset the white balance with something white inside the tank.