You should be able to do some good stuff with that camera.
A few pointers:
1. Clean the glass real good in and out.
2. Turn off lights in the house that may cause a light to show on the tank.
3. Use a tripod.
4. Turn off pumps and PH's. (no micro bubbles)
5. Find a good setting for your camera.
6. Turn the flash off.
7. Take lots of pics.
If you are going to be taking pics of moving fish then you will need some type of sports settings.
Play with your camera settings like your exposure, white balance, etc....
Usually out of about 100 pics I take, I only really like 10 or so.