Filamentous algae belong to the group of green algae. As a rule, green algae appear when the water quality is good, there is a high supply of nutrients and there is strong lighting. As the name suggests, thread algae form long threads. Given the right conditions, they are able to quickly overgrow everything in an aquarium.
The length of the threads can be different. In some species, threads a few centimeters long protrude from the ground, while other species wrap entire groups of plants with their threads. Sometimes small groups of filamentous algae settle directly on the plants in the root system. Especially if they get stuck on the plant leaves, they can damage the plants.
Causes of thread algae
Filamentous algae Photo: Mario Braun
Filamentous algae usually grow when the water quality is good and there is an oversupply of nutrients and light. Even if the conditions in the aquarium do not appear to have changed, small changes can trigger growth of filamentous algae. Such a trigger can Legs slight increase in temperature be in summer. Other triggers can be thinning out the plants and changing fertilization. In all of these cases, there may be a Imbalance between the consumption of nutrients through the plants and the supply of nutrients.
The following therefore applies:
As soon as more nutrients are available than are consumed by the plants, the excess nutrients are used by the algae, which then spread rapidly. If the water quality is high and there is enough light available, the filamentous algae benefit.
Filamentous algae often appear in aquaria with a few or mainly slow-growing plants, such as e.g. B. Java fern or Anubias are overgrown. Due to their slow growth, these are not able to consume enough nutrients from the water to represent real competition for the algae.
Measures against thread algae
1. Food competition
The best way to combat thread algae is to place as many fast-growing plants as possible in the aquarium, such as water friends (Hygrophilia) and swamp friends (Limnophilia). These consume the nutrients so that they are no longer available to the algae. It must be ensured that suitable nutrients (fertiliser, CO2) are available to the plants in sufficient quantities. In good conditions, such plants grow by 100 percent in two weeks.
If they become too long, the upper parts are cut off and re-inserted as long as there is still space. When the old plants become unsightly and begin to decompose, the old plants are pulled out of the ground and replaced with the cut off tops. With strong plant growth, the algae do not receive enough nutrients in the long run. It can take several weeks for the algae to go away. However, this does not result in a completely algae-free aquarium.
Land plants can also be used as food competition. The roots of these plants can be used directly or z. B. in a pot with expanded clay in the aquarium. Land plants remove excess nitrate from the water.
2. Reduce food supply
Filamentous algae Photo: Bruckmeier family
In the event of an algae plague, nitrate (NO3) and phosphate (PO4) should definitely be checked, since there is usually an excess of at least one of these two nutrients. An excess of nutrients can be reduced by reducing the input of nutrients into the aquarium. In particular, degradation products from feeding bring nutrients into the aquarium indirectly and in addition to plant fertilization.
A reduction in the amount of food helps here. If it is not possible to feed less per fish due to the demands of the fish, the stocking should be reduced. As a quick measure, excess nutrients can be removed from the aquarium by extensive water changes.
3. Use predators
Some fish species eat filamentous algae to a certain extent, e.g. B. the Siamese Algae Eater. Algae, however, prefer young green algae and do not eat older and longer filamentous algae. Also, catfish only eat the young shoots of the algae.
4. Decrease lighting
If the aquarium is heavily lit, the light intensity can be reduced at the same time. Shading can be an effective measure, especially when the sun shines into the aquarium. If floating plants are used, a higher consumption of nutrients is achieved at the same time as shading. Reducing the lighting time can also help. It must be noted that plants grow more slowly with lower light levels and therefore consume fewer nutrients. As always with algae, it is important to find the right balance between nutrient supply and nutrient consumption by plants.
Therefore, as an alternative to reducing the lighting, adjusting the amount of all nutrients, especially CO2, to the strong lighting can also be successful against thread algae. The stronger the lighting, the more CO2 is consumed. If there is not enough CO2 in the water, there is an imbalance in the nutrient balance, which benefits the algae.
5. Chemical algaecides
Fur algae Photo: Mario Braun
Even if thread algae can look very unsightly, you should never fight them with chemical agents. Chemical control worsens the water quality and reduces plant growth, and some plants are even killed off entirely. Algae can adapt to changing conditions better than plants. After using an anti-algae agent, the plants are usually weakened and most of the algae are dead. The decomposition of the dead algae produces new nutrients, which are now even more present in excess.
The surviving algae and spores of new algae can process this excess faster than the weakened plants and the basis for the next plague of algae is laid. The most important remedy against thread algae, competing plant growth, is thus impaired. Even if the filamentous algae recede in the short term, either the filamentous algae or other algae will come back in greater numbers in the period that follows.
Removal of thread algae
Longer thread algae can be wound up with a thin and rough wooden stick.
Threads that are stuck are plucked out or rubbed off with your fingers until you can pick them up floating freely in the water.
Special case: filamentous algae in the rearing tank
Filamentous algae are a very suitable plant for breeding tanks. They are able to continue growing even when other plants have already stopped growing due to a lack of trace elements. With their metabolism, they prevent high concentrations of pollutants, e.g. B. of ammonium, occur through the degradation of protein.
A prerequisite for this is, of course, an appropriate stocking density and lighting. They cover the water surface, provide shade on sunny days and thus limit the rise in temperature. In addition, excessive CO2 consumption and, as a result, an unwanted change in the pH value are avoided. The oxygen bubbles that get caught in the tangle of filamentous algae ensure that the rearing tank is well supplied with oxygen overnight.
Since the thread algae offer a very large surface, many different microorganisms settle in them, which serve as food for the young fish. If you carefully place additional feed with a pipette on a cushion of filamentous algae, you prevent the feed from sinking to the bottom too quickly. This is particularly helpful when surface-oriented juvenile fish need to be fed the smallest amount of live food.
Filamentous algae beginning to be covered by blue-green algae Photo: Frank Mersch
A tangle of thread algae offers the young animals a certain protection, e.g. B. the parents are still in the rearing tank.
If the tank overgrows too much, some of the filamentous algae can be easily removed from the tank. Indirectly, the pollutants consumed by the filamentous algae are removed from the tank.
Some fish species such as B. Cyprinidae (Koi) eat filamentous algae.