Green algae in the aquarium

Fleliaer, Ulvophyceae composite, CC BY-SA 3.0

The green plague

Algae in an aquarium are the nightmare of every aquarium owner. Excessive algae growth can be easily controlled with simple means, but an aquarium without algae is wishful thinking. Especially when setting up an aquarium for the first time, algae plague, especially green algae, can occur. The reason for this is the initially relatively unstable ecosystem during the running-in phase of the aquarium. There are about 4000 different species of green algae. Common to all of them is the green colour.

Most green algae (about 90 %) are freshwater algae. In a closed biotope like an aquarium, green algae can become a nuisance in no time at all. If they occur only rarely, they are actually an indication of good water quality.

However, if they get out of hand, the ecological balance in the aquarium will be out of balance. As algae are food competitors for aquarium plants, they quickly fall behind and are gradually displaced. Aquariums overgrown with algae have caused many an aquarium owner to give up.

What species of green algae are there?

Despite their great diversity of species, only six species of green algae play a role in the aquarium world:

  • Floating algae: These microscopic algae turn the water green. After a short time the water is so turbid that visibility is severely restricted. Suspended algae do not settle on furniture, panes of glass or plants in the aquarium, but, as the name suggests, float freely in the water.
  • Dust algae: This type of algae is known as the disc plague. This is due to the fact that they form a dusty, greenish coating on aquarium glass panes. Like floating algae, dust algae can also colour the aquarium water green.
  • Spot algae: The initially inconspicuous, punctual algae prefer to settle on aquarium glass. They spread quickly and sooner or later block the view into the tank. However, they also like to infest large-leaved plants.
  • Thread algae: The 5 to 20 cm long green filamentous algae colonise almost everything except aquarium glass. They grow on furnishings, plants, the substrate, filters and even on the hoses.
  • Fur, lint and hair algae: These three types of algae can be mentioned in the same breath because they not only look similar, they have similar properties. They cover furnishings in the aquarium, such as stones or roots, with their unattractive fluffy or fur-like coatings.

What are the causes for the undesired appearance of green algae in an aquarium?

Green algae love a lot of light and an excess supply of nutrients. Incorrect light conditions and too many nutrients in the water promote the uncontrolled spread of green algae. If sunlight is added to the aquarium lighting, the green algae literally explode. Sunlight is absolutely counterproductive.

How can excessive growth of green algae be combated?

The best weapon against green algae are their direct food competitors in the aquarium, the aquatic plants. Excessive plant growth prevents excess nutrients in the water and deprives green algae of their nutritional basis. Therefore, about 80% of the aquarium floor space should be covered with aquatic plants. At least 50 % of these should belong to fast-growing species such as water plague, hornwort, Sumatran fern and others. In addition, change water regularly (30 % tank content every 14 days), adapt fertilization to the plant consumption and feed to the needs of the fish. To give aquatic plants a growth advantage over algae, light in the blue and red wavelengths is recommended, with the red component being predominant.

Red wavelengths promote fast plant growth, blue wavelengths promote compact growth. Secondly, the duration of lighting is of crucial importance. Optimal for plant growth is 10-12 hours of lighting. Too much light is again an advantage for green algae. If the algae plague is already there, a pool cleaning by mechanical removal of the algae is also a possibility. A magnetic disk cleaner is best suited to free aquarium disks from point algae. The somewhat less stubborn dust algae can already be wiped off the panes with a sponge. Lint or fur algae that like to settle on furnishings such as stones and roots can also be scrubbed off with a brush under running water.

Thread algae on the other hand should be removed with a bottle brush. Finally, floating algae floating around in the water can be killed with a UV-C clarifier. Aquarium enthusiasts are also supported by algae eaters such as racing snails, shrimps, lesser catfish, sucking loaches or trunk barbs. It makes sense to keep some of these beneficial organisms in the aquarium.

One more tip: Do not use chemical agents! Proper water care is usually enough to keep green algae in check.

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