I'd suggest 3 or 4 bulbs (I have four), 2 being actinic, 1 being an 18k (pink) bulb. It'll add significantly to the color of your tank (and helps accent or offset the blue-hue that your halides are currently giving it). The bulbs I have are 48" (4x110w, 2actinic, 2x18k) and staggered in the canopy. Gives great accenting color to the halide lighting. You could go all actinic, but you wont really notice a difference between 2 and 4 actinic bulbs (other than minor increases in growth of coraline) - but you will enjoy the saturation of 18k's in addition to the previous.