What Causes Algae to Grow?

Algae grows in aquariums where there are excessive nutrients from plant and fish waste or inappropriate levels of lighting. Unstable water chemistry, inadequate partial water changes and infrequent filter cartridge maintenance also provide the perfect conditions for algal spores to multiply and bloom in your fish tank. Tackle the causes of algae, and you could prevent an outbreak of unsightly slime in your aquarium.

  1. Lighting Conditions

    • Too much or too little light causes algal blooms on aquarium glass and plants. Green algae grows quickly under excessive light conditions, and brown algae appears when there is insufficient light available. A balance of around 10 to 12 hours of daylight each day keeps both types of algae under control. If your tank is also exposed to additional natural sunlight, you may wish to reduce the number of hours you keep your tank lights switched on to prevent algae problems. Fluorescent lighting is less intense than metal halide lamps and helps keep algae to a minimum.

    Silicates in Tap Water

    • Diatom organisms are the cause of fluffy brown algae patches in fish tanks. Low light and silicates from tap water provide the ideal conditions for diatoms to flourish into a brown bloom on glass surfaces and tank decorations. Boost your aquarium's light levels to eradicate brown algae, and test new water for silicates before adding it to your aquarium to prevent a recurrence of diatoms.

    Overstocked Aquarium

    • If your aquarium has too many fish, the filter will become overloaded and unable to operate effectively. The resulting excess fish waste creates an environment rich in the nutrients algae needs to reproduce. Goldfish produce more waste than most cold water and tropical species, so take extra care not to overstock a goldfish tank. Change filter cartridges according to the manufacturer's recommendations to keep your tank running efficiently and observe appropriate fish stocking levels.

    Water Quality Problems

    • Uneaten fish food and decaying plant matter provide nutrients for algae and bacteria, creating poor water quality and unhealthy conditions for your fish and plants. Water treatments, fish medicines and even plant food can disrupt your water chemistry and encourage algae to flourish. Too much iron in the water leads to crops of thread algae. Water-soluble iron in aquarium plant food is safe and does not cause any problems when used correctly. Overfeeding plants can result in excess iron remaining undissolved in the water, promoting thread algae growth.