I kinda answered you comment before seeing it (took me a while to write the previous comment):
I prefer spreading the LEDs evenly over the tank, to make a "sky" effect. I know that means I won't have shimmer effect, and I'm ok with that.
About the colors, I want the red and blue to get a more realistic light. Furthermore, I believe I will have tetra neons, but honestly I didn't think of that before you brought it up