yeah, the ocean at night doesn't get totally dark, but it is rare for the room the fish tank is in to be totally dark either. I'd say no actual need for a "nightlight" but feel free to add one for effect. also, if you aren't doing it to help animals spawn, then you don't need to buy the expensive moonlight. just get a cheap flourescent or incandecent light. If i ever did that, I think i would put a red light over the tank, since the animals can't see the light, all the nocturnal animals would still be comfy while letting me watch them (no more flashlights!)