Having DSLR Camera has it's advantages. Reason: Image Quality,Adaptability,Speed,Optical View Finder,Large ISO range,Manual Control,Depth of Field,Quality Optics and a lot more.
Set your camera:
Aperture 4.5 TO 5.6 (Mostly I choose 5.6)
ISO 200 TO 800
White Balance would be best to play. and see which you prefer.
I usually choose Cloud,Shade and K choose temperature 6670.
The rest are automatic settings
Set your Aquarium:
Lights (Pink,Blue,White) Place on top of your tank nearest to the front view glass to allow dark Background make sure your light doesn't light the whole tank and using LED light helps me a lot just make sure you don't use powerful lights
No reflection. I usually take photos at night and only the aquarium has the lights turn on.
Would be best if the fish are hungry. Avoid feeding when taking photos.
Being alone when taking pictures has its advantages.
If tank with Background adding white light and a little yellow at the end of the tank back glass would make shadows in your BG.
Timing is Everything
It is better to clean your tank first.
Avoid sudden movement
Practice all angle and be Patience.
be aware of the fish movement. Expect and be ready to focus your camera.
I am not a professional camera man or proclaim to be one and not saying my photos are great or a professional 3D background maker. I am here hoping to have an Iphone5. It's a long shot.