You have to experiment. Try with the lights out. lights dim. Try your different settings on your camera too. It's hard to get a perfect pic sometimes. Make sure your glass is clean too. Your camera will actually focus on the water spots and streaks.
Matt, i aim the camera at a particular place in the tank then wait for the fish to stop there. i watch them alot so i know where they like to hang out. i also angle the camera slightly so i don't get reflected glare. the hardest part is keeping my arm and hand still.
nice gt.