(I have about 330watts of fluorescent light on my tank, so this may be different for you but...)

I like to turn on all of my lights first of all. I set my F-stop at F2.8 30. Usually this is an "expert" setting. The setting is usually darker but the bright lights will bring out good "hightlights" on the corals/fish. I do not use my flash.

Then I get right up on the glass, zoom in as much as I can without the picture getting fuzzy, and snap...

Good Luck... See my pics in the Gallery... Let me know what you think.