Algae Blooms in Reef Tanks

Algae are photosynthetic organisms that are found naturally in the wild and in all kinds of fish tanks. Diatoms, a particular type of algae, tend to appear suddenly in the tank when there is an excess of silicates and nitrates in the water, resulting in what is referred to as an algae bloom. An algae bloom typically results in a coating of brown slime on tank walls and decor that is unsightly but not difficult to get rid of.

  1. What Are They?

    • Aquarium hobbyists regularly refer to a sudden increase in the algae population in a fish tank as an algae bloom. Algae blooms typically involve the rapid growth and reproduction of algae cells due to an excess of nutrients, and they manifest in the reef tank in several different ways. Minor algae blooms simply seem to cloud or discolor the water, while severe blooms involve the formation of a brown slime on the walls of the aquarium and on aquarium decor.

    When Do They Occur?

    • Algae blooms occur when there is an excess of nutrients available in the water and when the conditions in the tank are optimal for algae growth. Warm temperatures and high lighting accelerate the growth of algae, but excess phosphates, silicates, and uneaten food can also lead to an algae bloom. Many aquarium hobbyists experience an algae bloom after their tank completes its first cycle because the nitrate levels in the tank are, at that time, quite high, but once the level stabilizes algae blooms should become less frequent.

    How Do I Get Rid of One?

    • The type of algae that accumulates on tank walls and decor during an algae bloom is typically blue-green algae or diatoms, and these types of algae can easily be wiped or scraped from tank walls. To remove algae buildup from tank decor, gently scrub nonliving rocks and other items with an algae scrubber and rinse well before returning them to the tank. Introducing algae eaters and scavengers such as snails to the reef tank is also an effective way to remove unwanted algae.

    How Can I Prevent One?

    • Most algae blooms occur due to an excess of silicates in the water. In reef tanks, the primary sources of silicates are the sand used as substrate on the bottom of the tank and the salt used to mix the water. If you use silicate sand in your tank, try switching to limestone sand or gravel and read, the labels on your marine salt to see whether it contains high levels of silicates. Other ways to prevent algae blooms include keeping tank lighting moderate, testing regularly for and making the necessary adjustments to phosphate levels, and avoiding the overfeeding of your fish so uneaten food does not build up on the bottom of the tank.