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Aquarium Algae Identification And Treatment

Updated on March 9, 2014

There are many types of algae, all share a common characteristic: they are non-vascular aquatic photosynthetic organisms.

Some organisms are near the vegetable Kingdom and other organisms are classified as bacteria or fungi.

The algae cannot be considered plants, because plants have vascular systems to drive the sap. The algae have a unique organ which serves as the stem and leaves.

The root system in the algae has the sole purpose of anchor the organism at the substrate or the rocks.

They have always been, are and will be present in the aquarium in the form of spores, waiting for the opportunity to proliferate as a plague.

The algae are always present in the aquarium in two categories:

  • The good ones
  • The bad ones

Aquarium Algae
Aquarium Algae

The good algae are the natural consequence of having a tank of water with food and a source of light.

They are present in small quantities, they are indicative of good water quality.

The bad algae are an indicator of poor water quality.

Those that cause problems are the Phaeophyta (brown algae dioatomea) and the Cyanophyta (green-blue algae).

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All abnormal growth of algae is a sign that something is not right in the biological balance of the aquarium. Usually the cause is not only one. Many different factors contribute to the proliferation of algae.

Under the strong illumination of the aquariums and with the presence of nutrients, the algae will appear inexorably. The most important nutrients that the algae need to appear are Silicates, Phosphates and Nitrates.

The Silicates and Phosphates enter to the aquarium if the partial changes of water are made with common tap water. The Phosphates are also generated inside the aquarium, since it is a product of the metabolism of the fish.

Algae Cyanobacteria

They are unicellular organisms that live isolated or in colonies. They are aerobic photosynthetic bacteria with chlorophylls A and B, although some species can not photosynthesize.

Factors that favor the appearance

  • Low amount of nitrates, because most of the species are capable of fixing the nitrogen
  • Low circulation of water, especially if there are few or no plants


  • They cover the substrate, the glasses, the decorative elements and the plants
  • Biodiversity with great capacity of adaptation
  • Some species produce toxins that affect other organisms


  • Addiction of nitrates up to 5-10 ppm
  • Increase water movement in the whole tank
  • Darken the tank for some days
  • Renew the water more often

Green Algae In Suspension

They are unicellular organisms with chlorophylls A and B. They form numerous colonies, they are known as Green Water. Besides the green algae in suspencion, we also find green point algae, which adhere to the glass surfaces, ornaments and plants.

Factors that favor the appearance

  • Abundant light, either natural or artificial
  • Large amounts of nutrients in solution


  • Clouds the water
  • They increase very quickly
  • They can cover large surfaces


  • Keep a balanced population of fish and plants
  • Darken the tank for 24 hours
  • Use germicidal lamps

Filamentous Green Algae

The filamentous algae have the aspect of hair or filiform groupings more or less upright. They can have harmful effects for the aquarium when it is present in large quantities.

Factors that favor the appearance

  • Recently mounted aquarium
  • Introduced through a plant


  • Compete with the plants for the nutrients
  • Cover the substrate and the plants


  • Remove the filaments manually
  • Use fish or crustaceans that eat the filamentous algae
  • Disappear when the aquarium has matured

Diatom Algae

They are unicellular organisms, free or forming colonies. They are characterized to present an external shell of silicon dioxide.

Factors that favor the appearance

  • Recently mounted aquarium
  • Excess of Silicate and Phosphate that can be introduced into the aquarium through the replacement water
  • High pH
  • Too short photoperiod


  • Any, because their massive appearance has a short lifespan (some days). They do not compete for nutrients with other aquatic plants


  • Increase the photoperiod
  • Change the water more frequently
  • Disappear when the aquarium has matured

Red Algae

All those that appear in aquariums are pluricellular and filamentous. They don't present a reddish coloration, but brown or blackish.

Factors that favor the appearance

  • Excessive accumulation of nitrogenated compound
  • Little content of dissolved carbon dioxide
  • High pH


  • They are very difficult to remove from the aquarium
  • Any algae remains can be focus of a new invasion


  • Change the water regularly
  • Lower the pH level and the hardness of carbonates
  • Add carbon dioxide


To eradicate the algae in an aquarium is impossible, some kind of algae will always be present either in planktonic form or ingrained on rock and substrate. Therefore the objective should be the reduction of the quantity of algae, not the total elimination.

When we detect a problem with a particular algae, the reasons that cause the formation should be analyzed and solved, rather than mechanical and repeatedly remove the algae without attacking the source.

The key does not lie in combating the algae, we should combat the causes that make them appear. The algae appear when the conditions of nutrients and light is favorable. Therefore to reduce or eliminate the excesses is the key to limit the quantity of algae.

Silicates and Phosphates: They diminish using water of osmosis and resins.

Nitrates: Control the population, the sedimentation and the circulation of water. Make frequent water changes or use denitrifying chemicals.

Light: The light is largely responsible of the type of algae. Enhancing the blue light allows photosynthetic invertebrates to grow and at the same time to control the algae.


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