Alaska_Phil

Jessy will have advice for you I'd bet.

You can increase ISO to 800 or so. Any higher and you'll end up with grainy pictures.
Try to avoid zooming in, because that changes the f/stop and thus slows down shutter speed.
Aim at a spot where the fish keeps swimming through, set the focus and wait for the fish to make the next lap. Shoot!
Shooting with a flash will definitely lock in a fish, but the colors will not match what we normally see.
The lower the f/stop, the better usually.

Have you tried googling how to set the white balance with your camera?

I'll look forward to her comments.

-I'll try the higher ISO, I was hesitent to go above 400 as my last camera started to get pretty bad noise at 800. However, I did choose this camera partly because it's reported to have low noise at higher ISO.

-Good call, I was zoomed in to better keep them in focus since I was using continuous, spot focus.

-I haven't looked on-line for white balance suggestions, duh! Should have been the first thing I tried. It manually sets it everywhere else just fine. I even put a big white plate in the tank and it still kept giving me a error message when I tried to manually set it. I'm guessing the color is outside it's range, but will check.

I'd say the white balance on your shots above looks pretty darn good though you may get better results with custom - though it can be a bit of work to set up properly. If I don't use custom white balance on my camera while shooting similar pictures, my blue chromis will come out purple!

I set the white ballance in post processing by selecting the white on the clown and the mostly white pipe in the background with the Chromis. Works pretty well, but it's interesting to see how much the results differer after selecting 2 areas that both appear white.