Fish tanks can be a beautiful addition to any home, but they must be cleaned regularly to stay looking lovely. One of the problems with any fish tank, professionally set-up and cleaned or not, is algae. Algae has a multitude of causes--one of them being the amount of light in the aquarium.
Type of Light
There are two types of aquarium lighting: fluorescent and metal halide. As fluorescent bulbs emit a lower intensity of light in relation to metal halide bulbs, they will thusly prevent sudden algae blooms that can occur with metal halide. The intensity of light is rated in degrees of Kelvin--normal aquarium fluorescent lights being between 5000 and 6500 degrees Kelvin. Depending on various factors in your aquarium, such as type of fish and depth, will factor into the temperature of light you should get.
There are also higher rated lamps such as 10,000 K and 20,000 K lights, which penetrate through more water before they are refracted. This means that if you have deep-water-fish, they will benefit from more intense light to get the nutrients they require. Also, if you have larger tanks with deeper water, higher intensity lights will reach through those depths whereas 5000 to 6500 K lamps will not.
There are three types of fluorescent lights, and using each depends on the type of fish and the type of tank that you have. There are standard fluorescent lights, which are usually used in small tanks under 55 gallons. They also should not be used if you are planning on having live plants in the tank (plants are recommended to keep the algae at bay, as well).
Standard fluorescent lights emit enough light to help fish, but not enough for keeping plants alive. Plants will actually eat nutrients in the water, like nitrate, which algae needs thrive, thus limiting its growth. There are also compact fluorescent lights, which are used for tanks that exceed 55 gallons of water. These bulbs are slightly more intense in their output and will sustain both plant and animal life.
Finally, there are VHO (Very High Output) lights, which are for very dramatic lighting conditions and for tanks that are 100 gallons or more. This type of lighting is recommended for the tank with a number of plants that you have in your tank. The higher the intensity of light, the higher the amount of algae that will be produced in your tank, so for best results, try to fix your tank in the 5000 K range (if your fish will survive, that is).
Duration of Light
The intensity and type of lighting in an aquarium affects health, stress, coloration and reproduction of fish, but it also affects the photosynthesis of plants and algae in your tank, thus affecting its growth and/or prevention. There are very few constants. One constant would be that fish, plants and algae require a certain amount of light and darkness day. It is best, no matter what kind of lighting you choose, to only have the light on for no less than 6 hours and no more than 10 hours a day. The fish, which thrive on structure and stability, need an ample amount of light to produce vitamin D. It is also important to not over-saturate the tank with light as it will cause more rapid algae growth. Algae, a plant, needs light to survive, and thus, will grow faster the more light it receives. First and foremost, control the amount of light. A timer is recommended for this action, as it will present the most accurate and stringent timetable for your light, and thus, limiting your algae from flourishing.