Hi HF. Since you are going to mount the lights 3' above the tank, I would probably use the 24" fixtures (since light spreads with distance). If we used 3' fixtures, lots of the light would miss the tank. I think three 24" fixtures in the Custom Orchid spectrum would be really nice. You can see the color in post #21 above. It is a mix of 6500K and Deep Red LEDs.