Different species of algae thrive under different lighting conditions. So there is not one specific light bulb to prevent algae. However, understanding the way aquarium lighting works can lead to control over algae.
Many types of algae thrive when an aquarium is over-lit. You can prevent this by using normal output or "NO" fluorescent light bulbs. Use less than 1.5 watts of power per gallon. In fish-only aquariums, you need only enough lighting to view your fish.
Plants and Lighting
Intense lighting -- combined with healthy aquarium plants -- can actually help keep algae in check. Aquarium plants are harder than they look; you need to take care of them for them to have a positive effect on algae. With their other needs met, higher plants thrive under high-output lighting like compact fluorescents, metal halide bulbs and LED arrays. Under intense lighting, thriving aquarium plants will out-compete algae for vital nutrients, starving the algae.
Controlling the length of time the aquarium receives light -- called the photoperiod -- can also help control algae. An electronic timer for your lights can make it easier to control the photoperiod. Set your lights for 6 to 8 hours per day. With a shorter photoperiod, any algae that need intense lighting will shrink back. If the problem persists, you can up the photo period to 8 to 12 hours per day. Some algae thrive under low-light conditions, so upping the lighting can discourage their growth. Sometimes experimenting is the best way to find the right amount of lighting for your specific tank.
Since different types of lighting thrive under different lighting conditions, you should also address other problems to prevent algae from thriving. All kinds of algae, regardless of lighting preferences, need nitrogen compounds to thrive, including ammonia, nitrite and nitrate. You can control nitrogen compounds by avoiding overstocking and overfeeding the tank. Monthly 25 percent water changes can also limit these nutrients.
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