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Blue green algae in aquarium

Blue-green algae

The name blue-green algae does not quite match the color ... the English name blue-green algae does. Actually, these are not really algae, but cyanobacteria, which contain chlorophyll and thus can photosynthesize like algae. Through photosynthesis they produce oxygen as a "waste product". However, since they do not have a cell nucleus, they do not belong to the algae, but to the bacteria.

Most of the more than 2000 known species of blue-green algae have a very special blue-green color, caused by blue phycocyanin and green chlorophyll. Cyanobacteria are very original living organisms and are among the oldest organisms of all. They are responsible for building the oxygenated atmosphere we know today, and there is even a theory that the green chloroplasts of plants were originally blue-green algae that migrated into plant tissue. A very popular representative of blue-green algae is the universally known Spirulina algae.

What is the catch?

But why are blue-green algae such extremely unwelcome guests in the aquarium? On the one hand, this is certainly due to the fact that they can not only form unsightly, sometimes very massive coatings, but also because many blue-green algae (not all, see Spirulina!) produce toxins, some of which are among the strongest natural poisons and can harm fish and invertebrates.

Recognizing blue-green algae infestation

An infestation of blue-green algae can usually be recognized by its intense blue-green color and carpet-like appearance. Blue-green algae are microorganisms, single-celled organisms, and the carpets they form have a soft, almost velvety texture. In addition, blue-green algae have a very characteristic fishy odor that can linger on your hands for hours. If in doubt, just take a quick sniff ... then you usually know. If you suck off blue-green algae clumps (Blog: Mulm absaugen) and put them into a clean glass, you will find a light green veil around the clumps the next day. "Normal" algae clumps do not develop this haze.

Causes of blue-green algae infestation

So how does an infestation of blue-green algae occur? Cyanobacteria are ubiquitous, which means that they occur practically everywhere in small to very small quantities. In almost every aquarium there should be blue-green algae, but they only appear in masses or multiply very strongly when the conditions are much more favorable for them than for other bacteria and for the plants, i.e. when they have little competition to fear. Blue-green algae often proliferate in aquariums where the bacterial fauna is suboptimal. In well-run aquariums with nice, vigorous plant growth and a healthy, stable microfauna, blue-green algae are never a problem! Nutrient surpluses promote a shift in the microfauna and microflora and can therefore also promote an infestation of blue-green algae.

Prevent blue-green algae from the outset

Prevention is better than cure - it is therefore very important to get the aquarium system running properly right from the start, or to get aquariums that are not running smoothly to function properly. This does not only include a balanced fertilization, a lighting adjusted to it and possibly also an additional CO2 supply, so that the plants completely consume the nutrients and there is not much left for the bacteria, but also a proper inoculation, so that a large spectrum of useful bacteria is available from the beginning. Inoculation with filter sludge from a running aquarium, which is so often recommended, is rather suboptimal. Over time, each aquarium develops a bacterial fauna adapted to the conditions in it, in which not all species are used. This means that it is possible that not all bacterial species will be introduced into the new tank. It is better to use a product like AT Nano Aktiv or Bacter AE, which contains the full spectrum of nitrifying bacteria. Another possibility: take half a teaspoon of unfertilized, unsprayed soil from the garden (not from a flower pot!) and slurry it in a glass of aquarium water. Let sediment settle and add the still-cloudy water to the aquarium. The nitrifying bacteria are actually soil bacteria, which can survive under water and whose properties we can use in the aquarium. So we also introduce enough different bacteria into the aquarium with such an infusion of soil.

Even a running aquarium can be inoculated from time to time to prevent the bioflora from becoming too one-sided. Preferably this can be done after cleaning the filter (only rinse, do not boil or use detergents).

Fight blue-green algae

But now we have an aquarium that we just couldn't get to work properly, and in it we notice a massive proliferation of blue-green algae. What to do?

Dark cure

Blue-green algae need a lot of light and die quite quickly if they don't get any more. Therefore, a two-week dark treatment is often recommended for aquariums with blue-green algae infestation. During the dark cure the cyanobacteria die. The higher plants usually survive this period without light very well, eventually the shoot tips become light.

If you had large amounts of blue-green algae in the aquarium, the huge mass of dead bacteria during the dark cure can stress the water so massively that the inhabitants can die from lack of oxygen. Therefore, all visible blue-green algae pads should be thoroughly vacuumed before a dark cure. The filter should also be cleaned (please rinse the filter media only with clear cold water), so that it can cope well with the additional biomass and does not become clogged. Additional aeration is advisable so that sufficient oxygen is supplied to the water.

Part of a dark cure is, of course, that the lighting is completely switched off. So that the blue-green algae really do not get any light, the aquarium must be darkened from all sides. To do this, use either a thick blanket or a cardboard box, which is simply placed over the aquarium.

The fish and invertebrates can remain in the aquarium during the dark cure. The fish and invertebrates can remain in the aquarium during the dark cure. During this time, the fish and invertebrates should not be fed at all or only very little, in order not to put additional strain on the water.

After the end of the dark cure, a large water change of 90% should be made and the substrate should be thoroughly vacuumed to remove as much dead biomass from the aquarium as possible.

This often solves the problem. It is important to optimize the aquarium system after the dark cure, i.e. to make the plants grow by an adapted fertilization and lighting and to help the biofilms to a greater diversity of species again by re-inoculation.

Basically, cyanos, like other bacteria, are sensitive to antibiotics. However, due to the increasing development of resistance and the difficulty of disposal, we strongly advise against fighting blue-green algae with antibiotics!

In case of very stubborn infestations it is actually better to completely redo the aquarium and try to get the system working properly (see above under the point "Preventing blue-green algae from the start").


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  • Hätte ich das mal früher gefunden ...

    Hallo!

    Ich kann gar nicht glauben, dass diese Beiträge so wenige Kommentare haben ...

    Ich finde sie sehr gut geschrieben (mit Fachkenntnis, aber verständlich) und total hilfreich. Besonders gut gefällt mir, dass die Ursachenbekämpfung im Mittelpunkt steht und von chemischen Keulen abgeraten wird. Auch die Einstellung, dass Algen in den Mikrokosmos Aqaurium hinein gehören und sogar dekorativ und nützlich sein können, hat mich angesprochen. Viele Beiträge zur Algenbekämpfung, die ich anderswo gefunden habe, waren eher oberflächlich und kommerziell orientiert. Auch im Dehner oder Obi habe ich nicht wirklich hilfreiche Antworten erhalten.
    Vielen Dank für diese Reihe!

    Liebe Grüße

    Rebekka


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