I have a 6w fluro affixed to the ceiling, next to a 150w metal halide pendant. It comes on for an hour before and for two hours after the MH switches on and off. I have a lot of catfish, mostly Brochis and Corydoras, plus some Hypancistrus & Synodontis and Glass Cats, they all become particularly active when the night light is on. I also added it to help a group of Chalceus settle, as they tend to get a bit flighty when the lights go out. I've also noticed the Pantadon butterfly seems a bit more active and redily takes food under the moon light.