Here are the two shots. The top shot is from my dSLR, the bottom is from my wife's point and shoot set to "Simple Mode" and has the flash turned off. I did not use a tripod for either shot, instead I just leaned on some available furniture. I tried my best to get the same level of zoom for both and no editing has been done to these shots, both were imported into Lightroom (I shoot in RAW on the dSLR) and both were exported with no editing.
The most noticble differences
-dSLR took a better overall exposure (normally I do a lower my exposure by a full stop due to how bright the lights are but for this purpose there was no exposure compensation).
-Point and Shoot is over saturated, but this comes part and parcel with most point and shoots.
The water looks cleaner in the point and shoot shot, but I was in the tank messing around a bit between takes so please disregard that aspect.
Environmentally all I did for these shots was to turn the lights off in the room and close the curtains (taken after dark). No flash used in either shot.
Based on these results, I would recommend the following:
-turning off the lights in your room
-closing the doors/curtains
-turning off your flash
Taking these basic steps should get you what your looking for no matter the camera. The only variable I could not test was flat fronted tanks as mine is curved, there is a possibility that if you see too much of your own reflection in the shots that you may have to take the picture at a slight angle, but only experimentation on your end will determine that.
f9, 1/50, ISO 3200, White Balance Auto, shot in "aperture priority"
Point and Shoot:
f4.7, 1/8, ISO 200, White Balance Auto, shot in "Simple Mode"