Dividing the Day Whether over a desktop nano-reef or a 6,000-gallon public exhibit, well-simulated moonlight can add an entirely new dimension to the aquarium habitat. For sure, once you’ve installed a good moonlight, nocturnal fishes (such as cardinal fish) that once seemed boring will now have a certain appeal. So, that part about timing your tank lights to match the natural photoperiod? While good for the animals, it does pose one problem for those who work into the evening; the keeper hardly ever gets to see the tank with the lights on! Overall, moonlights add some interest to the nighttime aquascape and truly give the hardworking aquarium keeper a little something to come home to.,Image via iStock.com/greenp By Kenneth Wingerter Lighting is one of the most important components in a saltwater fish aquarium system. This is particularly so if you keep photosynthetic organisms such as corals, macroalgae and tridacnid clams. The most effective marine aquarium lighting system is the one that is most controlled. Reef Tank Lighting Schedule One of the major lighting parameters that is most commonly controlled is photoperiod. Put most simply, in the context of an artificial environment, photoperiod is the tank’s lighting schedule. Aquarium photoperiod is controlled by timers (ranging from cheap household plug-in units to highly capable hardware/software located either in the unit or in “the cloud”). Generally, timers are set to operate the lighting at its highest intensity during midday when ambient light (light pollution from the room) is strongest. With your aquarium lights timed to match the ambient photoperiod, strong light pollution won’t inhibit the normal nighttime activities of the nocturnal creatures nor the rest of the diurnal (i.e., daytime active) creatures. But sunlight is not the only source of illumination in nature. Moonlight, too, has a huge influence on a coral reef. True, it is tens of thousands of times weaker than sunlight. It is indeed far too weak to support photosynthesis, for example. Still, it is just bright enough to guide reticent night dwellers from shadow to shadow. It even keeps sleepy diurnal fish from getting spooked out in the dark. And, perhaps most importantly, it widely serves as a major environmental cue—a signal. It seems a little light is better than none at all.