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Blue Green Algae - BGA - How To Get Rid Of Cyanobacteria In Aquariums

Blue Green Algae - BGA - How To Get Rid Of Cyanobacteria In Aquariums

Most of you have experienced Blue-green algae in an aquarium at one point. How to get rid of them from your planted aquarium? Why are the so-called Blue-green algae (BGA), not algae but bacteria?.. and many more interesting facts you will learn here...

Algae Or Bacteria?

Cyanobacteria is the correct generic name for the so-called Blue-green algae, often just called BGA in the aquarium hobby. Since Blue-green algae and BGA are much more familiar terms, we will continue to use them for better legibility. BGA don’t have a true cell nucleus like algae and thus belong to the bacteria as prokaryotes.

They have probably inhabited the earth for more than 3.5 billion years, making them one of the oldest forms of life. They were also probably the first living organisms to carry out photosynthesis, which produced oxygen. There are about 2000 named species that cannot be determined precisely with the naked eye.

Blue-Green Algae Use Larger Range Of The Light Spectrum

The photosynthesis of the BGA is similar to that of plants and algae. However, Blue-green algae not only use the part of the light spectrum used by plants and real algae, but they can also utilize other light spectrum ranges via an additional protein complex, the phycobilisomes. BGA can use light in the wavelength range of about 500 to 600 nm for photosynthesis, whereas plants and algae cannot. This particular feature makes Blue-green algae much more effective in their growth, and they can successfully colonize distinctly low-light areas. In nature, this is, e.g., the underside of river boulders and deep and dark layers in lakes. In the aquarium, such locations can be found at the bottom or in low-light areas like shaded hardscape areas.

blue green algae in lake

Occurrence Of Blue Green Algae In The Aquarium

According to experts, the Blue-green algae Oscillitoria splendens is mainly found in freshwater aquariums. A nutrient minimum is sufficient for this species to grow, and it enters the aquarium, for example, via plants, substrate, or even spores from the ambient air. Even in a sterile aquarium, they can begin growing - although not necessarily visibly - after 20 to 30 days. If invisible, BGA filaments can still be detected using a microscope.

Unfortunately, there are no clear findings or studies on why Blue-green algae occur in freshwater aquariums. In addition, there may be multiple underlying causes simultaneously, so the causal investigation may take longer to identify the reasons. We would love to give you an ultimate solution, but there is no such thing. However, some countermeasures can help greatly limit or prevent the occurrence of BGA.

Characteristics Of BGA

Blue-green algae are usually easy to identify, thanks to their typical characteristics. They form smeary, foil-like coatings that are not rich green but rather dark green with a bluish tint and sometimes even appear blackish. These coatings feel greasy and slippery and can be easily removed from an infested surface. When BGA coatings extensively cover planted areas, the plants may still produce some oxygen, and bubbles can visibly form under the coating. But BGA's most unmistakable and distinct identifier is its foul, musty smell. Anyone who has smelled it once will remember this stench and know if it is BGA.

Another characteristic, which hopefully will never show up noticeably in your aquarium, is toxins that some species of Blue-green algae produce and release into the water. However, the amounts of toxins are so small that you do not have to worry about the life of your livestock. At low levels of BGA, the toxins are insufficient to cause harm — no need for panic. Nevertheless, you should keep the situation and the spread of BGA under control and always initiate countermeasures in case of surface spread.

blue green algae microscope photo

Things That Can Lead To A Blue-Green Algae Bloom

  • Weekly water change routine is not consistently implemented
  • Insufficient aquarium maintenance
  • Livestock numbers too high
  • Overfeeding

What Preventive Measures Are Advisable

  • Although BGA are very reliable in the aquarium, an evident nuisance infestation can be counteracted with preventive measures:
  • Regular maintenance with a weekly water change of at least 50%
  • Appropriate livestock concerning aquarium size
  • Feed consciously! In other words, feeding daily but in small portions is better than vice versa. Food that is not utilized by the livestock, but lies on the bottom and decays, contributes to an increase in phosphate levels and can promote BGA and algae growth. If small amounts of food end up on the bottom, don't worry, this is usually unavoidable and will not lead to a BGA or algae bloom. If you have shrimps in the aquarium, you don't have to worry about a few food particles remaining on the bottom; the busy crawlers will gobble them.
  • Sufficient and even flow through the entire aquarium. Achieving a uniformly strong flow at every point in the aquarium is impossible. There will almost always be areas with little flow, e.g., at the bottom or due to obstacles like hardscape. Just make sure that you provide your aquarium with the best possible flow. Optimization is the motto.
  • Not only in the start-up phase of an aquarium is it worthwhile to use certain aquarium bacteria products to build up a beneficial bacterial culture for the biological system. Every time we intervene in the aquarium's biological system, it can impact the bacterial culture, which may lead to its decimation. The reason for this can be cleaning and inactive phases of the filter, cleaning in the aquarium, introducing new materials such as hardscape, and extensive plant pruning. Especially after such interfering measures, it is highly recommended to strengthen the bacteria culture with appropriate bacteria products. Because "good" bacteria compete with the BGA for space.

blue green algae in aquarium

When And Where Blue-Green Algae Can Appear

Generally, BGA likes to settle in low-flow areas of the aquarium. This may well have a trivial reason. Because BGA hardly adheres to the colonized surface, zones with a stronger flow seem unsuitable for colonization. Apart from such strong flow areas, BGA feels comfortable settling almost everywhere.

  1. BGA in the substrate

Often, Blue-green algae can be discovered first between the aquarium glass and the substrate before they appear elsewhere in the aquarium. The growing conditions seem particularly good there, with relatively little water movement and plenty of available nutrients in the soil and from decomposing organic waste.

  1. Weakened Biological Ecosystem

In addition to the aquarium filter, all other inside aquarium surfaces - aquarium glass, substrates, hardscape, plants, etc. - also provide a colonization surface for the bacteria that are important for the biological equilibrium.

BGA may start spreading if the "good" nitrifying bacteria do not use parts of the filter media and other available surface areas for whatever reason. Most reasonable for such bacterial-free surfaces include a recently set up aquarium, new hardscape, new plants, and using bacterial destroying drugs for livestock treatment. You should know that some medical preparations do not only eliminate the disease-causing pathogens but also the beneficial bacteria!

  1. Nutrient Imbalance Between Nitrate (PO4) And Phosphate (NO3)

Experience has shown that a nitrate deficiency with simultaneous phosphate excess can also be responsible for increased BGA growth. Nitrate and phosphate belong with potassium (kalium) to the macronutrients and are consumed more significantly by the plants than the micronutrients. A nitrate deficiency not only slows down the plants' growth enormously but other nutrients, such as phosphate, can no longer be metabolized by the plants (law of the minimum). Everything that is not consumed is available to the BGA and algae as a nutrient source.

  1. High Water Temperatures

Bacteria love a warm environment and can increase as temperatures rise. Of course, this also applies to BGA. With rising water temperatures, unfortunately, the conditions for BGA also improve, which can become problematic, especially in the summer months. If your livestock allows it, we recommend keeping the aquarium temperature below 24 °C.


In general, before taking any action against BGA - the same applies to algae growth - we advise our customers to consider what causes can be ruled out. Such an exclusion process is a good starting point for a targeted and solution-oriented approach to remedying the cause.

Example: Let's assume it is July, and in your aquarium, which has been running for ten months, there have been minimal BGA films between the aquarium glass and the substrate for quite some time. It has not spread any further or required significant intervention so far. But then you notice that BGA is starting to extend beyond the substrate to the plants.

Now think about what could have caused this. Has something changed in the flow, or has it become less? If yes, then look for and eliminate the cause of the flow reduction. Have you made any changes to the aquarium in the past weeks, like, fertilizer addition, water temperature, technical equipment, hardscape, plants, or major cleaning measures, e.g., filter cleaning? For this time, the answer is no, and your next step is to look at the thermometer. The temperature displayed is 27 °C, but it usually is around 23 °C maximum.

The reason for the temperature increase in the aquarium is the increased room temperature due to the summer heat. This is possibly the cause or at least one for the increased BGA occurrence. You should find a solution to keep the water temperature even on hot summer days. How you can achieve a constant temperature despite summer heat and other valuable means for various occasions will follow.

blue green algae in aquarium

What Immediate Measure Should Be Taken

It is advisable to siphon all visible BGA films from the aquarium with a significant water change to remove as much BGA as possible. Repeat this procedure every other day, or everyday if necessary, and add a bacterial product to the aquarium afterward. Please follow the manufacturer's dosage instructions.

Measure In Case Of Heavy Infestation

In case of a heavy infestation with Blue-green algae, we advise you to do a blackout. Before introducing such a blackout, you should implement the Immediate Measures mentioned before.

Using "The Fogging Method"

The fogging method is a targeted measure to combat BGA with spot dosing. A liquid substance harmful to BGA is applied to the affected areas in the aquarium using a disposable syringe. A blunt needle is advisable in case of an infestation in the substrate.

For the solution to act at the desired location for some time, water flow should be avoided as much as possible. Therefore, turn off filters or pumps before treatment. The technical devices can be reactivated after a few minutes of exposure time.

blue green algae spot dose with syringe

Products That Can Be Used In Case Of BGA Infestation

It is important to note that before using any anti-algae product, you should read the manufacturer's recommendations. With some products, too high a dosage may harm the livestock! Also, it should be clear that any substance used against BGA cannot eliminate the cause. Anti-BGA solutions provide a temporary measure against BGA growth to prevent invasive spread until the underlying cause can be eliminated.

Ultralife Blue-Green Slime Stain Remover – Ultralife Blue-Green Slime Stain Remover has been specially formulated to combat the problem of blue-green slime, using a secret mix of natural ingredients, supplements and biological accelerators to provide the ultimate blue-green slime stain remover. It is easy to use, just mix a small amount of aquarium water, with the appropriate amount of product, using the included measuring spoon according to your aquarium size, and then merely add straight to your aquarium water. 

Easy Life Easy Carbo & Seachem Excel – These solutions contain liquid carbon for the plants but are basically a disinfectant with the agent glutaraldehyde. The plants can metabolize these liquid solutions but are no substitute for a regular CO2 supply. Both products are not explicitly designed for use against BGA but work with their disinfecting property against bacteria. In case of Pay attention to the dosage instructions!

ADA Phyton Git SOL – Phyton Git SOL is an antibacterial agent against blue-green algae (BGA), based on Phyton Git PLUS, and consists of plant extracts with antiseptic components. Phyton Git SOL works very efficiently by directly treating affected areas. The "fogging method" and spot dosing are recommended for the application.

ADA Bacter 100 – This product is a powdered substrate additive that contains more than 100 species of bacteria in a dormant state. The bacteria only become active when added to the aquarium and contact with water has occurred. ADA Bacter 100 provides a natural and safe method of controlling BGA and is ideal for BGA infestations between the aquarium glass and substrate. The Bacter 100 bacteria are a food competitor for the BGA.

Söchting Oxydator 3% Solution – This product is a 3% stabilized hydrogen peroxide solution and can be used effectively against BGA and other algae. Before use, please be informed about the correct dosage because the wrong dosage is very dangerous for livestock. Please read our article about the Söchting Oxydator 3% Solution. The "fogging method" and spot dosing are recommended for the application. Plants, especially mosses such as Riccardia sp., are usually more sensitive to higher concentrations.

Do you still have questions about BGA or the presented products?

Our customer service is at your disposal. We are also delighted to assist you with any other aquarium-related topics.

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