Macluvr, Quick questions....Are you using a tripod and external flash? I see people come out with some really nice fish tank shots when they have a lens that will focus close up on the tank or zoom in on fish inside the tank. Also see them us the external flash and fire it threw the side of the tank, so you don't get a reflextion off the glass.
Love your tank setup, i see your pictures have a shutter time of 1/25. I've always found this a bit too slow for moving fish but they seem fairly sharp. I guess they don't move that much?
Ah the machine gun approach
I would try to keep the shutter speed up to about 1/60th of a second. If you can get more light in the tank that will always help as well, just don't get to much heat and cook the fish.
Ah the machine gun approach