Rod I agree with Alex, change the white balance try different ones you should have five different settings along with manual mode which is a user defined white balance to be used with a grey card under the current lighting (don't worry don't use the manual mode). The great thing with digital you can always delete and try again. Do do this though turn off all other lights in the room. You said you tank is in your office, florescent lights can give off very strange color cast which can effect your photos. Also don't hesitate to up you ISO, that camera is using the new Digic III chip low noise and great color. Keep trying and keep posting those great shots.