Discus Fish Lighting Requirements

Discus fish, native to South America, are shy, sensitive animals with narrow ranges of acceptable living conditions. They need high quality, warm water, proper lighting, and an aquascape that supports their reserved nature. A discus aquarium needs to have a variety of light intensities available to balance optimal plant growth with fish behavior and color rendering. If the aquarium owner doesn't manage the light properly, algae will grow unchecked, the fish will be stressed, and the colors in the tank won't look right.

  1. Light Measurements

    • Thomas Giovanetti states in his book "Discus Fish," "The goal is to get both the proper spectrum and intensity of light over the aquarium."

      The "spectral," or color characteristics of light is measured in Kelvins. The sun at noon on a clear day has a Kelvin (K) temperature of 5,500 K. This is a bluish white light. The lower the Kelvin temperature, the more red the light will appear. The color rendering index can also provide some guidance as to how the color will appear to the human eye. The ideal bulbs are about 5,000 K color temperature with a color rendering index (CRI) of 90.

      Supporting healthy plant growth is another key consideration. The light available must include the appropriate "photosynthetically active radiation" (PAR) to grow a diversity of plants and prevent excess algae growth. Typically the higher the Kelvin, the lower the PAR. Experts recommend 400 to 700 nanometers PAR.

      Intensity refers to the total amount of light available as measured in "lumens." A light bulb has a basic lumen output, but that value is amplified as light bounces off the reflector hood. A densely planted aquarium needs 120 to 200 lumens per gallon.

    Lighting Options

    • Aquarium light bulbs will have the above measurements listed on the box. However, you will still have to decide between fluorescent and metal halide bulbs.

      Fluorescent lights are inexpensive, easy to replace, give off little heat and come in a wide variety. Different bulbs used in combination can approximate ideal conditions. Often hobbyists opt to use fluorescent fixtures to augment metal halide fixtures.

      Metal halide lamps are more expensive to set up but less expensive to sustain because the bulbs last much longer. The light can penetrate deeper into the water so you're able to get more lumens per watt. These bulbs provide very good color rendering but they also get very hot.

    Photoperiod

    • The length of time the lights are running each day is called the "photoperiod." The daily photoperiod needs to be a consistent 10 to 12 hours under ideal light conditions followed by 12 to 14 hours without external light.

      Longer periods of time are not necessary as it spurs the growth of algae but doesn't actually help the desirable aquatic plants. Additionally, discus fish are prone to stress from extended light conditions. Stress reduces their resistance to disease.