tripod will do wonders, and they are cheap, so its a worthwhile purchase if you are looking for good pics. next, shut off all the lights in the house / room, leaving the tank lights on.
Get a large chip, so you can take photos at the largest setting.
Canon should have a Manual mode, where you can make slight adjustments.
switch the quality to super fine.
if its like mine, the AE should have an autoset feature, that will adjust the white balance. set that after you have adjusted your house lights.
change the shutter speed to the fastest possible setting.
if it has multiple drive mode, try the manual focus one, so when you take the picture, it takes three pics at once, each at a little different focus to help the chances of landing a great shot.