Blue-green algae © Frank Mensch
Blue-green algae are among the most troublesome types of algae in the aquarium. In extreme cases, they cover the ground, plants and objects as a slimy, foul-smelling mass that suffocates all the plants underneath. Their color varies from brown-green to blue-green to dark green. They sometimes multiply explosively. They often seem to prefer areas with little current and a low redox potential. There may be nutrient sources beneath these sites that will provide them with the nourishment they need. Blue-green algae are only firmly attached to the subsoil in a few places. Together they form a stable interwoven mat 1 – 3 mm above the ground, under which the necessary nutrients can circulate and thus all blue-green algae can benefit. The mat is closed relatively tightly at the top so that no nutrients can escape. The mat is furry at the bottom, creating a large surface area for optimal use and distribution of nutrients. Accordingly, they also like to settle on the mat filters through which the air flows slowly.
The blue-green algae found in aquariums are vibrating algae. Under the microscope you can see that the individual bacteria, which look like rods, swing back and forth and can thus quickly change their location.
Blue-green algae should be combated as early as possible, especially since some species also excrete toxic substances that can possibly harm the aquarium inhabitants. Plants usually do not survive a heavy infestation of blue-green algae for long, since blue-green algae are strong competitors for food. Suction catfish that eat blue-green algae may die. According to other reports, an unusually large number of catfish and other fish died during blue-green algae plagues without any particular sign.
Strictly speaking, these are not algae at all, but so-called cyanobacteria (Source: algen-im-aquarium)
Since there are many different types of blue-green algae, which all have different requirements, the causes and countermeasures can hardly be described in general terms.
Filamentous algae beginning to be covered by blue-green algae Photo: Frank Mersch
while e.g. For example, one aquarist suspects a lack of nitrate as the cause of blue-green algae, another aquarist suspects too much nitrate to be the cause. They occur in soft and hard water. They grow on sandy soil as well as on gravel. Also, water hygiene does not always seem to play a role. There are numerous reports of blue-green algae in clean water and in aquariums where the water is changed frequently. Nevertheless, even if blue-green algae appear, the water quality should be checked first, as they tend to appear if you overfeed and neglect to change the water. The possible causes and measures are therefore described below, even if they sometimes seem to contradict each other. Since it is hardly possible for us aquarists to recognize the type of blue-green algae present, only the most probable causes can be identified and countermeasures tried one after the other. However, the dark cure seems to be the most effective measure, which also has few negative side effects. Several measures can also be carried out at the same time in order to achieve success more quickly. However, it is then later impossible to determine which of the measures taken was successful.
Causes of blue-green algae
In contrast to plants, some types of blue-green algae can utilize atmospheric nitrogen. If the plants do not have enough nitrate or ammonium, the plants cannot compete with the blue-green algae.
Potassium deficiency is also suspected of promoting blue-green algae.
Too much lighting can also lead to blue-green algae. It is often observed that blue-green algae do not appear in the shade of plants. The shadow edge often forms a sharp dividing line between bright zones where blue-green algae grow and shadowed areas where no blue-green algae can be found.
Other species seem to prefer dimly lit aquariums and can be controlled with more lighting.
Blue-green algae Photo: Frank Mersch
The fact that blue-green algae often develop on the ground supports the thesis that blue-green algae develop when too many nutrients are constantly washed up from the ground. The nutrients get into the soil through fertilization with special fertilizer for the substrate or through organic substances that have previously penetrated the soil and are now rotting, some of which even form toxic substances. As long as this source of nutrients exists, new blue-green algae will keep appearing, even if they have been carefully removed beforehand. Accordingly, blue-green algae prefer to settle in places where nutrients are washed out by the circulation of water through the soil. Floor heating, so-called floor floodlights, filter systems installed in the floor and coarse gravel promote the circulation of water through the floor and thus the removal of nutrients.
Similarly acting sources of nutrients can be roots, malfunctioning filters and other sources where organic matter is rotting due to lack of water movement rather than being broken down by aerobically or anaerobically acting organisms. In particular, the occasionally modern soil filters push substances introduced into the substrate, including substrate fertilizers, upwards in excess into the aquarium water.
Other possible causes are insufficient water flow and too little or too much CO2.
Measures against blue-green algae
dark cure
During the dark cure, the aquarium is completely darkened for about a week. For this it is all around z. B. taped with black cardboard, or put a dark blanket on and around the aquarium. Of course, the lighting stays off during this time. With an oxygen stone, additional oxygen is brought into the water. Existing CO2 systems should be switched off during this time. Photosynthesis comes to a standstill due to the darkness and the plants consume correspondingly less CO2. Apparently, blue-green algae cannot tolerate the lack of photosynthesis. The fish are not fed during this time.
Before the blackout, e.g. B. by suction, as many blue-green algae as possible, as well as rotten or heavily infested leaves are removed from the plants. Mulm should stay in the pool.
Fish and other inhabitants are not harmed by this darkening. Often the plants are even stronger after such a cure than before. However, you should be careful with very sensitive plants and take them out of the aquarium beforehand and clean them separately if necessary.
After the cure, the dead blue-green algae are removed with one or more vigorous water changes. Then fast-growing plants are used and the plants are fertilized. The addition of CO2 supports the recovery process of the plants. The aim of the measures is to change the entire aquarium climate in such a way that the plants like it better than the algae. Since plants and algae are in constant competition, the algae have a harder time the better off the plants are and vice versa.
Fertilize with nitrate or ammonium
Nitrate or ammonium eliminate any possible lead of the blue-green algae in the supply of nitrogen. The plants thrive better and take nutrients away from the blue-green algae.
Check phosphate content
If there is less than 0.2 mg phosphate per liter of aquarium water, the plants no longer grow properly and blue-green algae use the other nutrients that the plants do not use. If the phosphate content is too low, it can easily be increased by feeding the fish more. More specifically, phosphate can be added with Tetra’s Torumin, which contains plenty of phosphate. Care should be taken here, as too high a phosphate content can also lead to increased algae growth. A content of approx. 0.25 mg per liter of water is a good guideline.
Add potassium salts
The addition of potassium salts is also said to be a way to combat blue-green algae. 10 to 30 mg of potassium per liter of aquarium water are recommended. However, adding potassium does not work in every case. Potassium supplements may only work if they correct a corresponding nutrient deficiency in the plants since potassium is a plant fertilizer. However, too much potassium can lead to brush algae. In this case, brush algae disappear when the addition of potassium is reduced.
Stronger lighting
If blue-green algae occur in dimly lit aquariums or in the shade of plants and objects, stronger lighting can eliminate the blue-green algae plague. If the lighting is increased, care must be taken to ensure that the plants also have a corresponding number of nutrients at their disposal. Otherwise there is a risk of exchanging the blue-green algae plague for increased growth of green algae. It is advisable to use an iron test to measure when and how much fertilizer needs to be added under the changed light conditions.
deploy predators
The tricolor medaka (Poecilia melanogaster) and the algae tetra (Parodon pongoense) are said to eat blue-green algae. Apple snails and tower snails also eat blue-green algae, but not always. According to a report, dwarf shrimp of the genus Neocaridina also eat blue-green algae.
introduce food competition
In addition to plants, other food competitors can also be introduced into the aquarium. It will e.g. B. reported that the addition of starter bacteria has led to the death of blue-green algae. Adding filter sludge from an aquarium without blue-green algae seems to have a similar effect. Either the overall climate in the aquarium is changed by the many new filter bacteria in such a way that it is no longer beneficial for the blue-green algae, or the microclimate created by the blue-green algae is disturbed. The temporary cessation of water changes or less frequent water changes can also lead to competition between the bacteria due to the increased water load and cause the blue-green algae to disappear.
patience
If the supply of nutrients is too high due to rinsing out of the substrate, only patience or a new installation of the substrate will help. Only when the organisms that break down these nutrients in the soil have settled in the soil does the blue-green algae lose their food base. If the soil is gravel, sand can be sprinkled into the spots where the blue-green algae settle as a quick measure. Since this changes the water circulation, the nutrients usually escape again at another point. The blue-green algae disappear from their original location only to reappear elsewhere. In the long run, this measure is therefore just as little recommended as sprinkling sand all over the gravel floor. Since the rotting substances remain in the ground, they will re-emerge sooner or later. Due to the changed flow conditions, it may even be more concentrated in some places than before, so that blue-green algae grow all the more in these places.
Hydrogen Peroxide (H2O2)
Hydrogen peroxide is considered…