Instructions
Research the lighting needs of each plant and animal species in your aquarium. An ideal fish tank is not a hodge-podge "community" aquarium, but a conglomeration of carefully selected species with similar requirements for lighting, setup and water chemistry. Ensure that all species in your care have similar lighting requirements.
Select an appropriate Kelvin rating for your aquarium. A Kelvin rating describes the spectrum of light emitted by a bulb. A T5 bulb may have a Kelvin rating of 5,500, 6,500, 10,000 or 20,000. Short wavelengths of 5,500 and 6,500 have a reddish tone, while longer wavelengths are blue-violet in color. Shorter wavelengths are ideal for most green freshwater plants, but red and brown plants require the intense rays found in 10,000 K and 20,000 K bulbs. Tall tanks also need a higher Kelvin rating because longer wavelengths can penetrate to the bottom of the tank.
Determine the output needs of the species in your care. In general, freshwater plants need a T5 bulb that emits 2 to 5 watts per aquarium gallon. A planted 29-gallon tank, therefore, requires a T5 bulb that emits at least 60 watts of energy.
Determine if a T5 fluorescent bulb will meet your aquarium's lighting needs. These generally emit 15 to 40 watts and have Kelvin ratings from 3,000 K to 10,000 K. If these are not appropriate for your tank, consider a compact fluorescent bulb, which emits 10 to 100 watts and comes in a wider range of Kelvin ratings.
Look for high-output and very-high-output T5 fluorescent bulbs. These are very bright and emit 20 to 160 watts of energy. Very-high-output fluorescent bulbs can have Kelvin ratings as high as 20,000 K; they are most appropriate for red and brown freshwater plants and for very tall, deep fish tanks.
Consider using a metal halide bulb if there are no other T5 options meeting the needs of your aquarium. A metal halide bulb is very expensive but emits an impressive 175 to 1,000 watts of energy. Metal halide bulbs are popular among reef enthusiasts because they provide the intensiveness and spectrum most similar to sunlight, but they are rarely necessary for freshwater planted tanks.
How to Choose T5 Bulbs for Freshwater Plant Aquariums
A T5 aquarium bulb is any piece of lighting equipment measuring 5/8 inch in diameter. Contrary to common misconceptions, measurements such as T2, T5 and T8 do not measure the strength or spectrum of lighting, but the thickness of the bulb itself. Your freshwater aquarium's setup, resident species and aesthetic preferences will affect your ideal choice in T5 bulbs. Speak to a consultant at your local aquarium supply store for advice tailored to your specific needs.