Effect of Aquarium Lights on Plants

Different types of aquarium lighting can have profound effects on the growth of aquatic plants. Choosing the best lighting system depends on the types of plants being grown and the size of the aquarium. Light intensity can determine how frequently the plants need fertilizing and pruning. The two types of lighting systems are fluorescent and metal halide. Each has advantages and disadvantages.

  1. Plant Types

    • Aquatic plants vary in their lighting needs. Some, such as sword plants (Echinodorus), require high light levels. Others, such as crypts (Cryptocoryne), will grow in low light. Still others are intermediate between these two extremes.

    Aquarium Size

    • The deeper the aquarium, the more light intensity is reduced toward the bottom. A 24-inch deep tank requires four times the light intensity of a tank only 12 inches deep, other conditions being equal.

    Pruning Frequency

    • Because the rate of plant growth is proportional to the light they receive, plants under bright light will grow more rapidly than in a more dimly lit environment. Aquarium keepers who want to avoid frequent pruning can reduce light levels to slow the plants down.

    Fertilization

    • Because plants grow faster with more light, it follows that they need more food under higher light intensities. Aquarium keepers generally have to experiment with the fertilizer regimen to determine the optimum for a particular aquarium. Start with a small amount and increase the dose gradually, as too much fertilizer may produce algae growth.

    Fluorescent Lighting

    • Fluorescent aquarium lighting systems cost less initially. The replacement lamps are relatively inexpensive, too. However, they may not provide enough intensity for every situation. Select a fixture that accommodates at least two, and preferably four, lamps.

    Metal Halide Lighting

    • Metal halide aquarium lighting systems cost considerably more than a fluorescent system for the same tank. However, metal halide provides the highest intensity available. It is the lighting system of choice for large tanks, or those more than 20 inches deep.