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Lighting Your Aquarium

Lighting is a fundamental aspect of freshwater and saltwater aquariums. A good basic rule to follow is to provide two  watts of lighting per gallon for fish-only aquariums, two to five watts per gallon for freshwater planted aquariums, and four to eight watts per gallon for reef aquariums.

In its most basic role, aquarium lighting allows you to observe aquarium inhabitants. But more importantly, proper aquarium lighting provides vital energy to photosynthetic plants and animals. As the primary light source (and in most cases, the only light source), proper aquarium lighting is essential for any system that contains photosynthetic organisms such as plants, anemones, or corals. Lighting also influences fish behavior and physiology and is vital for the overall health and well-being of the entire aquarium

The most common fixtures available are Normal Output fluorescent (NO), Very High Output fluorescent (VHO), Power Compact fluorescent (PC), T5 High Output (T5HO) fluorescent and Metal Halide (MH) light fixtures. NO flourescent fixtures are the least bright and Metal Halide fixtures are the brightest.

NO fluorescent fixtures are generally all you need for a basic fish-only aquarium. They are usually the least expensive and will provide enough light for viewing your fish. If you plan to keep live plants or live corals in your tank you will need a lighting system that will provide enough light for the plants and symbiotic algae found in corals to photosynthesize. This can be accomplished using multiple NO output bulbs over the tank or high output lights such as a VHO, PC or T5 fluorescent fixture or a MH system.

Bulb will be available in different spectrums or colors listed by a Kelvin (K) temperature scale. The lower end of the K range bulbs will generally be a greenish (5500K) to a yellow color (6700K) color and are a good spectrum for growing live plants. The 10000K bulbs are generally a crisp white color. They are not as good for your plants but still provide beneficial light without the yellow look. The higher K rating bulbs (12000K-20000K) have a bluish hue and are used for saltwater tanks. Most of your NO bulbs will simply be labeled “color enhancing” or “plant grow” bulbs for an easier selection. For a fish only system, the color enhancing bulbs are generally your best choice.

For a fish only system you can keep your lights on for as long as you wish with the average time being around 4-8 hours per day. If you are having issues with severe algae growth in the aquarium you can lower the amount of time the light is on to help inhibit the algae growth. For live plants the lights should be on 10-14 hours per day to allow the plants plenty of time to photosynthesize.

Use timers for a more stable environment. Fish are creatures of habit and enjoy stability, including lighting. By putting your lights on timers to come on and off the same time every day your fish will generally be less stressed and overall healthier.

Don't wait for your bulbs to burn out before replacing them. Bulbs will slowly dim over time and lose their effectiveness, even if you can tell they are dimmer. Lights over a planted aquarium should be replaced every 8-12 months and for a fish only system the bulbs should be changed about every two years.