Proper lighting is crucial to maintaining a saltwater aquarium. Most marine fish that people keep in their tanks come from warm shallow seas, where light is generally abundant but varies depending on geographic position and environment. You can usually go with “all-purpose” aquarium lighting, but in some cases you have to fashion your lighting to fit the creatures you plan to keep.
The waters in tropical and sub-tropical regions receive abundant sunlight throughout all seasons, but fish are exposed to different levels of light depending on their surroundings. In mangrove systems the water is usually filled with organic particles, mud and other detritus, which allow a limited amount light to penetrate. Reefs, on the other hand, are also found in tropical regions, but crystal-clear waters allow light to penetrate easily.
Because light requirements vary, aquarium systems are usually sold without lights. Make sure to purchase only bulbs specifically designed for an aquarium system and expect to purchase them regularly. Bulbs should be exchanged every six months or so because their intensity and quality will fade with time.
Usually, you can buy a hood to go with your tank that will allow for many different kinds of lighting systems. Or, if you are changing your entire set-up, ballast units or conversion kits are available to account for any special bulbs. Timer units that switch the lights on and off automatically are also becoming a standard accessory.
Since most lights will put out heat, you can inadvertently be cooking your fish if ventilation under the hood is poor. Even worse, if the housing gets too hot, it could start a fire. Make sure that the hood or lighting fixture is large enough to account for this waste heat. Some aquarists install small fans to help circulate the air and get rid of the heat. If you’re initially setting up a tank, give the lights a test run and see how hot they get. If you can burn your fingers when you touch the hood, it’s too hot.
Check that the light housing is strong, a perfect fit on you tank, and securely fixed to the aquarium, especially if you have a curious cat or a “hands-on” youngster who could accidentally knock it free.
The Right Bulbs
There are many ways to light a saltwater tank, from fluorescent bulbs to metal halides. A key factor in choosing a bulb is its K-value. The higher the K-value, the “cooler” the light that the bulb produces. However, watch out. Bulb manufacturers have marketed the K-value into a dollar-value and have priced their bulbs to imply that the bigger the K the better. Thus higher K-ratings are more expensive. For comparison, daylight is rated at about 6,500K, which is generally enough for fish.
If you invest in a reef system, you will definitely not want to skimp on a lighting system. Be aware that bigger lighting systems often require a second look at your ballast unit – you may have to upgrade to something sturdier.
If you are planning to have a coral or two in your tank, then you must plan for a minimum of at least four fluorescent bulbs, although six are preferable. A general rule of thumb to keeping hard corals, which need light for the photosynthesizing symbionts living in their tissues, is about two to five watts per gallon. Soft corals don’t mind the lower light levels that four bulbs produce, but for long-term care of hard corals, this amount of light won’t do.
Another advantage to metal halide lighting is entirely aesthetic: the light isn’t as strong and so it falls unevenly on your reef, creating shadows and exaggerating any movements in the aquarium. Shadows of the water’s gentle ripples undulate across the reef under this light, most closely recreating the natural scenery. Those who have done it will admit that the initial hassle a metal halide lighting system requires is well worth this beautiful effect.