How To Eliminate Thread Algae In The Aquarium

thread algae

Find out 8 easy ways to control thread algae in your aquarium today

Thread algae can ensure that the water values ​​in your aquarium are kept in balance. Unfortunately, there are usually not just a few algae and before you know it, the threads, which are up to 20 centimeters long, wrap around entire groups of plants and decorative objects. 

Find out here how an algae plague occurs and 8 ways to immediately eliminate thread algae.

How do I recognize thread algae?

Thread algae belong to the group of green algae and come in very different forms. While some thread algae develop thin threads up to 20 centimeters long, other forms are more short-threaded with a length of up to 5 centimeters.

Sometimes they are more like cobwebs; sometimes they are reminiscent of small, green wads of cotton wool. Depending on the species, they wrap their threads around whole plants and decorative objects, proliferate as long threads out of the substrate or settle in small groups directly on the plant roots.

thread algae
Thread Alge

How are thread algae harmful?

If the thread algae get out of hand in the aquarium and overgrow plants, stones and other objects with their green threads, it not only looks ugly, but is also harmful to both the infested plants and the entire ecosystem of your aquarium.

  • Anevent causes a spike in nutrients such as Nitrogen or Phosphorus
  • Thealgae utilise this sudden increase in nutrients and rapidly reproduce
  • They use up the trace minerals andnutrients and die as suddenly as they appeared. This sudden dieback results inan increase in bacterial decomposition and loss of normal oxygen production andultimately, fish death

Algae are much less demanding than most other aquarium plants and spread rapidly even under rather unfavorable conditions. As a result, the nutrient content of the water is further imbalanced, other aquarium plants wither and the living conditions for the fish deteriorate.

That does not mean that you have to keep your aquarium free from algae – this goal would be utopian, because there is no such thing as an aquarium completely without algae. However, you should be careful not to let the algae get the upper hand.

What is the relationship between oversupply of nutrients and thread algae?

Despite all care and regular care, it can quickly happen that the green pests spread too much in the aquarium. Even small changes in light intensity, the duration of lighting or the water temperature, for example due to increased solar radiation in summer, can cause algae to multiply.

As a rule, there is an oversupply of nutrients, i.e. more nutrients are available than can be used by the aquarium plants.

The thread algae take advantage of this imbalance: They utilize the surplus nutrients and spread rapidly. In order to remedy this imbalance and permanently ban the thread algae from the home aquarium, it is important to know the causes of the nutrient excess. Who just got the algae out of theIf you have removed the aquarium without fighting the cause of the algae infestation, the green threads will soon be found again.

What is thread algaue and how to get rid of it

Why should you first check the water values?

If you discover thread algae in your aquarium, you should first check the water values. Test strips or digital measuring devices are available in specialist shops or on the Internet with which you can determine the content of CO2, nitrate and phosphate in the water.

In the case of massive thread algae infestation, there is usually an excess of at least one of these three nutrients. The CO2 value should by no means be below 5 milligrams per liter, in the ideal case it is between 10 to 20 mg / l. A nitrate level above 20 mg / l is also a cause for concern. In this context, you should also check the tap water, because the nitrate content is often too high here.

If your tap water contains more than 50 mg nitrate per liter, you should mix it with osmosis water before changing the water. Mixing the tap water with such “pure water” is also recommended if the phosphate content is too high. Waterworks often add phosphate to tap water to prevent the calcification of water pipes. Too high a phosphate level can also promote algae growth.

What are the causes of thread algae?

The reasons for an excessive supply of nutrients are of course not only due to excessively contaminated tap water. Light intensity, duration of lighting, plants, fish stocking and feeding also have an impact on the nutrient balance. Finding the exact cause therefore requires a little detective work for the aquarist.

As already mentioned, the three water values ​​nitrate, CO2 and phosphate provide decisive approaches in the search for the reasons for the algae infestation. An increase in a value is usually triggered by the following errors or changes.

How to eliminate thread algae

The nitrate value is too high?

  • The tap water is too heavily polluted with nitrate. If the water is changed extensively, too much nitrate gets into the aquarium.
  • Fish are fed too often: The excess of unused fish feed and the increased excretion of the fish (the more feed is consumed, the more feed is naturally excreted) can increase the nitrate content in the water.
  • The fish population in the aquarium is too high: the more fish in the tank, the more excretions and the more nitrate gets into the water.

The CO2 value is too high?

  • The aquarium is too bright: The lighting time is too long or the location of the aquarium is incorrect (e.g. too much sunlight).
  • The number of plants is not optimal: There are too few plants in the tank or they have been thinned out too much. Instead of fast-growing plants, there are primarily slow-growing plants such as Anubias or Java fern in the aquarium.

The phosphate level is too high?

  • The tap water is too rich in phosphate.
  • Plants have been fertilized too much: Many fertilizers for aquarium plants contain phosphate.
  • The feed contains phosphate. Many types of dry or frozen food contain phosphate, which can be particularly problematic in the event of overfeeding.


Not only an oversupply, but also a lack of nutrients can trigger increased algae growth in your aquarium. If the CO2 content in the water is too low , this has a negative effect on plant growth, which in turn benefits the resilient algae. 

A CO2 value that is too low can usually be traced back to an insufficient supply of light, for example from a lamp that is too weak or too short a lighting period, or to incorrect vegetation (plants that are growing too slowly).

8 ways to immediately eliminate thread algae

Once you have identified the cause of the thread algae, it is now time to eliminate them as quickly as possible. Unfortunately, algae do not disappear overnight and so patience and consistency are required not only when investigating the cause but also when combating the algae infestation. After all, the nutrient content of the water cannot be brought into balance in the short term. Unfortunately, there are no immediate measures to permanently drive the thread algae out of your aquarium.

However, the sooner you intervene, the sooner you will master the green plague. The following steps are recommended as first steps:

1. Removal of thread algae

Long thread algae can be easily rolled up and pulled out with a brush or a thin, rough wooden stick. You can pluck or rub off shorter threads on plants or on the ground with your fingers. You can fish free floating algae out of the water with a sieve or by hand.

2. Cleaning the decorative objects

You should remove stones and objects and scrub them thoroughly under running water.

3. Carry out a water test

As already described above, you should – if you have not already done so – carry out a comprehensive water test with test strips or a digital measuring device.

4. Carry out a water change

To do this, change about 30 to 50 percent of the water. If the fresh tap water is too heavily contaminated with nitrate or phosphate, mix this with osmosis water.

5. Use fast-growing plants 

Well-growing plants are essential for a functioning ecosystem with balanced water values. The best-known plants for combating algae are hornwort and stem plants, such as the water friend (Hygrophilia), the swamp friend (Limnophilia), the waterweed, the water comb or the water front.

6. Reduce feeding

Fish often need much less than their owners believe. Make sure that you only feed as much as your fish actually eat. Fish can also tolerate a feeding break (for example one fasting day per week) and is very beneficial to the water quality.

7. Use algae eaters

There are fish that can help you fight thread algae. Tetra, flag cichlids, Siamese algae, armored catfish or certain types of shrimp eat the green threads. However, you should not use too many of these algae eaters, as the other plants and the water quality could also suffer.

8. Shorten the lighting time

If you come to the conclusion that incorrect or excessive exposure is the reason for the algae infestation, you can also temporarily darken the aquarium. However, you should not overdo the darkening, as this will not only weaken the algae, but also the other plants. Basically, an exposure time of 12 hours is sufficient for the plants to grow well. After this time, turn off the lights or take a break from lighting of one to two hours a day.

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