I know i am new, and i know i am grave digging this topic, however, i would like to add a few more things to Kens list.
The first is that taking a pic with the flash on is a big no no. No matter what, it will disorientate the colour of your tank, and usually destroy the effect, so i would say, no flash.
Second. When you take a pic, focus on an area that is either, really bright, or semi dark. Never do both. The light will in effect, take over from the darker areas, and your picture will suffer. The camera is not like our eyes, it can not distinct between dark and light, it will only take what is the strongest and go from there.
Third. When taking a photo, i find that the best shots are always taken at night when there is little to no light in the room besides that of your tank. This means that there will be nothing to distract from the focus of the shot.
Fourth. When taking a shot from below up, the reflection of the light on the surface of the water is again, enough to destroy an amazing shot, try to change position so that you get as little of the light in as possible.
Fith. If you are having problems with the glass reflecting your image without the flash on, do not be afraid to get the lens of the camera right next to the glass so that it is touching it. This will limit the amount of reflection and increase the focus of your picture...
Hope you are able to make sense of all of that and that it helps