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Algae Guide

Green Aqua Algae Guide

There will inevitably come a time in your life when you will see some form of algae appearing in your aquarium. Some of you may even start to think about abandoning this beautiful hobby because of the algae bloom, saying that it takes just too much time to fight algae and keep the aquarium nice and clean, or you might become very frustrated of the ugly image of your aquarium full with algae. Nobody wants to watch that day-by-day... This should just not happen!

Algae appearance (algae bloom) shows some kind of "biological system failure". It tells us loud and clear that we made a mistake (or a series of mistakes) during the planning phase, or it tells us that we have a setup problem with the otherwise well-suited equipment or that some environmental factor is just not right. Point is, we should not fight algae! We should find the CAUSE and we should eliminate that!

We have good news: with gaining some expertise - or occasionally spending just a little more money on your aquarium equipment to support the equilibrium - you will surely be able to maintain an algae-free beautiful aquascape. It is never a good idea to only treat the symptoms, it is not enough to remove the algae (if it can be removed at all), and it is absolutely the worst idea to use algae remover chemicals (biocides). Find the flaws in your system instead. It might sound magniloquent, but our best advice is to listen to Nature and do not repeat all the things you know you did right - we all tend to do that: "I have good filtration, good CO2, my light is enough, and I still have algae". That will not solve your problem, but it will only protect your ego. Always blame yourself and know that Nature is always right - and always stronger than your will and your ego. We learned that the hard way. We stay humble.

OK, so what causes algae to appear?

In short: the presence of light and ammonia. The more light we have (and modern, high-tech aquariums have a lot of light), the less ammonia is needed to trigger algae-bloom. This is why beginning aquascapers see more algae after setting up their aquariums than traditional, low-tech hobbyists.

Problem is that ammonia can not be just "eliminated" - unless you make bigger, daily water changes in your aquarium - but that will also be a symptom cure. Our goal is to find out what causes the ammonia levels to spike in our water - and this is where things start to get more complicated. Ammonia appears as a result of decomposing organic elements in your water. This can be of multiple sources: dirty or inefficient filter, fish that died and remained undiscovered, decomposing plant leaves, accumulated mulm, etc.

They used to think for years that algae bloom is caused by excess Nitrates and Phosphates. Modern science has proven that this is not true at all – except of the extreme levels of Nitrate (over 50 ppm) and Phosphates (over 5-10 ppm) that will limit plant growth and thus causing leaves to start decomposing. You will not even be able to see this decomposition process with your own eyes, even microscopic-level rotting can cause so much Ammonia in the tank that algae will appear.

Others will think that algae is caused by nutrients. If you have not been using professional plant fertilizing before (like Green Aqua fertilizers) and start dosing regularly, you might start to see algae blooming and you might get the wrong idea that the whole mess is caused by nutrients. This is simply not true. Algae are just like plants - but on a lower evolution level: they like the nutrients. If you had an aquarium that was full with non-invasive algae and you start fertilizing it properly, algae will also start to thrive - together with your plants. A previously insignificant algae problem - that was invariably caused by another issue - will start to be visible.

The solution for the problem is not to stop dosing or starting to cut back on fertilizers. The solution is to eliminate the cause. For example, if the cause was a simple lack of nutrients (with the previous fertilizing method) then you should continue dosing and removing the algae until they just disappear (plants "overgrow" algae). If the original problem was not (only) the lack of proper nutrients than regular dosing and algae removal will not be enough, as part of the original problem still persists. You will have to find the additional causes in this case.

This guide will help you find the different causes for algae appearance and will help you address those causes. Luckily the different types of algae will indicate slightly different causes so you will have a clue where to start looking for the source of trouble.


Algae Removal Products


Algae types


Brown Algae - Diatoms (Diatomaceae)

Causes: low-level lighting in old, non-CO2 aquariums, or high levels of Ammonia in newly set-up tanks. It likes the presence of Ammonia and Silicates - the latter can originate from the sand, bad-quality gravel, stones not suitable for aquarium use, zeolite-based filter material and can also come from the tap-water. It has two common types: the first creates a slimy brown surface, the other comes as thin brown threads. It is not a "dangerous" algae type, it can be removed easily (by just wiping the aquarium glass) and it disappears easily. Algae eaters as Otocinclus Affinis will consume it and remove it quickly. In low-tech (non-CO2) aquariums you will need to increase light intensity (now the hours of illumination) - but please keep in mind that increasing the light will result in higher CO2-, and fertilizer need. With new high-tech aquariums it will just disappear by itself with time. Try to remove it physically and help the spread of nitrifying bacteria. Appearance in older, properly lit aquariums will show bad water quality and presence of Silicates.


Green Spot Algae - GSA (Choleochaete)

Small, round spots on hard surfaces - most visible on the aquarium glass. It will also appear on slow-growing plants, typically the Anubias-types. It is the algae of healthy aquariums, you will probably see some of it in all aquariums.

It likes strong lighting and blooms when Phosphate and/or CO2 levels are low. It sticks strongly to different surfaces so algae eaters will not really remove it. The Zebra Nerite Snail and it's family will remove some of it - but not very efficiently. Use an Algae Scraper to remove it from the glass and replant the slow-growing plants that tolerate low lighting in shady areas. With medium-light aquariums you should pay attention to regular water changes and efficient filtration, with strong lighting check the efficiency of your fertilizing regime and CO2 injection. As it is mostly caused by Phosphate (PO4) deficiency, please start to add more phosphate to address the main cause.


Green Dust Algae - GDA

This is an algae mostly present in high-tech planted aquariums. The really small green spots form a dust-like layer on aquarium glass and hardscape. This type of algae will not usually grow on plants. The exact origin of this type of algae is not really known, it is a type of zoospores that consists of individual cells capable of movement. It is mainly caused by low CO2 levels and low nutrients. More frequently seen in new aquariums.

Algae Scrapers are not a solution as the cells removed from the glass and floating in the water will stick to hard surfaces again after some time. Addressing the symptoms: You will need to let these algae grow without disturbance for 10-20 days! It will form a thick green layer that can be removed (sucked out) in big chunks, and if the root cause is addressed, it will not return later.


Green Fuzz Algae (Oedogonium)

All thread algae are indicating low- or fluctuating CO2 levels! Carbon-dioxide fluctuation can be caused by uneven CO2 levels (because of a pH computer for example) or a timer that was not set up correctly (CO2 levels will have to reach the desired level at the time when light - even natural light in your room - appears). The Fuzz Algae is a thread algae that grows thin threads of just a couple of millimeters on plant leaves. It indicates that the plants are suffering (leaves rotting locally) due to mainly nutrient deficiency (for example the local lack of CO2 that is not distributed in evenly by the flow in the whole aquarium). It can appear on old, and damaged leaves. Algae eaters and Amano Shrimp will eat it.

To address the cause, you will have to ensure the proper CO2 levels, and time you CO2 injection according to the lighting period (start 2-3 hours before-, and switch it off together with the lights). Please take the natural light in consideration too. CO2 need of plants can rise due to a cast of light at mornings for example - even if your lamp will switch on at noon.


Green Beard Algae - GBA

All thread algae are indicating low- or fluctuating CO2 levels! Carbon-dioxide fluctuation can be caused by uneven CO2 levels (because of a pH computer for example) or a timer that was not set up correctly (CO2 levels will have to reach the desired level at the time when light - even natural light in your room - appears). The Green Beard Algae is presumably a more virulent form of Green Fuzz Algae. The fine longer threads will attach to plants and hardscape. It can grow a couple of centimeters and form a dense green coat on their surface. It can be very decorative at times. Algae eaters will like it very much.

It can be difficult to remove mechanically, as it attaches strongly to surfaces. the threads are slimy and weak. It is a typical algae of fish tanks without plants, but it does not necessarily indicate bad water quality. In planted tanks it is indicating that the lighting period is too long (reduce it to 8 hours) or CO2 levels are too low, or there is not enough Nitrate in the water.


Black Brush Algae - BBA (Audouinella sp.)

Often called as Black Beard Algae - this is a very difficult type to get rid of! The small black, dark-grey or reddish hairballs will grow in clumps or patches of fine black tufts with a length of half a centimeter. It likes places with strong flow, it sticks to hardscape and submersed equipment (filter in- and outflows, internal filters, etc.) If you have hard water, the Calcium will get incorporated into the threads and algae eaters will not like it. The Siamese Algae eater and Amano shrimp will eat it, but they are not efficient. In a strongly lit aquarium in can be caused by the lack or uneven distribution of CO2, final solution will be to address that. With weak lighting it will help to let the water rest before water changes. Tap water (and fresh RO water) are rich in CO2 - this will favor these algae but slow-growing low-tech plants will not profit from it.

This is one of the most difficult algae to remove. It appears with no apparent cause even in older, very stable lush tanks. Most of the times the only solution is to remove the spots - one-by-one with heroic scrubbing, and that would not at all guarantee that it is not going to come back. Removal is helped immensely by this tool: ADA Pro picker. Using a liquid carbon additive (switch the filter off, apply locally with a syringe) will help kill this algae. It will turn red and whitish before disappearing.


Blanked Weed (Cladophora)

Some will blame the moss-ball for spreading the Cladophora infection. The truth is, that the moss-ball is indeed a type of Cladophora, but it is different from the one that causes the Blanket-Weed invasion. The moss-ball is slow-growing, so it can also be easily attacked by algae, that will thrive on the surface of the ball.

The Blanket Weed is a rough, branching algae that looks a like some kind of moss. It will stick hardly in a point and spread from there, so it can be isolated and removed from the middle of your plants. If it contaminates your moss, you will need to trim it down hard. Algae eaters will avoid it. Improving flow and CO2 will help, weaker lighting will push it back relative to the plants. This algae will not spread in air, so you can completely avoid it if you use only lab-grown plants in your aquarium.


Algae Eaters


Green Water

Green Water is caused by floating algae. It can be composed of multiple types of organisms, from real green algae like Chlorella to flagellates. It appears very quickly and it is difficult to get rid of it. It is caused by an Ammonia spike, nutrient-level problems or low CO2. It is generally triggered by some kind of water quality problem - for example the Ammonia released in the water after you disturbed the substrate. Improving water quality (with water changes for example) will not solve the problem. Once the algae have bloomed they will survive even in low-nutrient conditions. You can do a 4-day blackout to solve the problem but bear in mind that the algae that have been killed might cause Ammonia spikes. Always ensure good aeration with blackouts. Using UV filters is also highly efficient against Green Water. The third option is the usage of a diatom filter that will clean these algae from your water in hours and they will not produce any Ammonia that might cause further trouble. Making a diatom filter is easy, just get some Diatomaceous earth (diatomite) and use it temporarily in your filter. There are other chemical solutions that might seem easy to apply but they are far from ideal because they might kill algae but they can be of adverse effects to your sensitive fish or plants.

The cloudy but not green water is caused by floating ciliates (also known as infusoria among aquarists). Some of these tiny creatures will possess chlorophylls so they can use light and thrive in low-nutrient conditions too. You will have to perform a blackout combined with a UV filter treatment and diatom filter. Green Water has its own advantages in the aquarium hobby: you can use that as food for hatching Artemia and Cladoceras (water fleas).


Water Silk (Spirogyra)

It forms, long and strong threads with a smooth touch. It is very decorative under microscope, the thread is a green spiral stretching for the whole length. It's appearance indicates a previous Ammonia spike that was caused by a fish carcass or by disturbing the gravel or substrate. Once it is present it is difficult to eliminate because the needs of these algae are very similar to plants. A blackout and liquid carbon cure will usually help. Algae eaters do not like it in particular, but will eat it if there is no other algae in the aquarium.

Sima békanyál – Spirogyra (Water silk)

Green Thread Algae

It has long, span-size threads. It can be collected by coiling them on a toothbrush but it is almost impossible to eliminate them from mosses. Some say they appear as a result of excess iron in the water that can be caused by unbalanced plant nutrition or ingredients from root tabs that were somehow dissolved in bigger quantities into the water. It frequently appears together with hair algae. Change big amounts of water and rethink your dosing regime. The Siamese Algae eater and Amano shrimp will eat it.

Zöld cérnaalga (Green thread algae)

Hair Algae (Rhizoclonium)

Thin, cotton wool-like greenish-greyish threads stretching for a couple of centimeters. They will not stick to surfaces. It frequently appears with low nutrient-levels. It is also connected to low CO2 levels and low flow. Algae eaters will love it, it is a good complementary food for all herbivore fish. It is advisable to clean the gravel once it appeared. Strong flow will limit its growth.

Hajalga – Rhizoclonium (Hair algae)

Staghorn Algae (Compsopogon sp.)

It forms threads of grey or bluish horn-like branches. It typically appears on leaf edges in the form of fluffs. It likes areas closer to the surface. It sticks hard and the surface is really greasy so it is almost impossible to remove. High Ammonia levels, low-flow and nutrient balance issues will favor the appearance of this algae. Clean the gravel and the filter if it is clogged and the flow is weaker. Cut the infected leaves. Apply liquid carbon additives with the filter stopped for a couple of minutes - the algae will turn red and die.

Agancsalga - Compsopogon sp. (Staghorn Algae)



Blue-Green Algae - BGA (Cyanobacteria)

Caused by low nitrate-levels, ammonia spikes and dirty substrate or filter. Blue-green Algae are in fact photosynthesizing bacteria. There are many types that can appear in the aquarium. Some of them will thrive in high nitrogen-level substrates with decomposing organics, others will appear in completely nitrogen-free environments. Most common are the blue-green-, grey- or black-colored types that will form a plaque on the substrate surface and plants. This plaque can be easily sucked out with a hose during water changes but it will usually reappear if you do not address the cause.

It also frequently appears between the glass and the substrate or plants - at the bottom of the aquarium - along the front glass and sides. Once it appeared it will start to spread quickly and can become dangerous to your ecosystem. The invasion is also characterized by a bad smell around your aquarium. The blue algae can produce toxins that can kill the fish and plants, so their spreading should be stopped quickly.

blackout will help as a symptom treatment, but if useless, we need to use antibiotics as a last resort. Because we are dealing with bacteria here, the erythromycin antibiotics is effective, but that will also kill the nitrifying bacteria in the substrate and our filter too! This is a drastic measure. If you choose to walk this path, you have to look at your nitrate balance carefully and try to help recolonizing your filter and substrate with filter bacteria additives. If the BGA does not appear to be very invasive, you can try to remove it with regular water changes and by using fast-growing stem plants. If nitrate levels were low in your aquarium, you might want to increase that to 10-30 ppm.

Kékalga - Cianobaktérium (BGA - Blue-Green Algae)


Surface Scum

Surface scum is not really algae - in fact it is bacteria! Plants in the water will release protein when under stress (caused by CO2, nutrient or even temperature issues). The completely transparent protein is lighter than water so it will accumulate on the surface forming a thin layer - serving as ideal media for different types of bacteria. Just like a lab Petri dish... At the end, you will in fact see the bacteria, not the protein layer.

This protein layer will also give life support for certain algae - this will transform it's color to green. The version without alga will look opaque. Besides the unattractiveness the Surface Scum has another adverse biological effect: it limits the gas exchange on the surface. This can result in the CO2 and oxygene imbalance and lead for further algae issues as filter bacteria also need a lot of oxygene to thrive.

It is very important to remove surface scum on a regular basis. Besides taking care of the general balance of your ecosystem and limit the protein production of plants you can take a couple of measures to remove this layer. You can use a Surface Skimmer to continuously or temporarily remove surface scum or you can elevate lily pipes for the night to break the water surface. Strong aeration will also remove it. Frequent water changes, good mechanical filtration, regular (but not continuous) use of activated carbon will also help. As a quick removal method place a kitchen towel on the top of the water and quickly remove it, repeating this method with new towels. This will completely remove the Surface Scum.

Olajos vízfelszín, felszín-hártya (Surface Scum)

Cloudy Water

The white (opaque) water or cloudy, milky water is most of the times caused by excess, overgrown number of useful bacteria (not dangerous to humans). In new tanks it can be caused by excess use of water treatment products (bacterial colonies), in old tanks it is a sign of bacterial imbalance. We might experience it after cleaning the filter - this is when the balance is more fragile.

In most of the cases the cloudy water will disappear by itself after a couple of days if we have good filtration and good biological balance. Water changes will also help getting the balance back - but will not address the root cause.

If the cloudy water does not go away, use a UV filter for treating the symptoms. The UV light has a sterilizing effect so it will kill all bacteria in the water. (The UV filter can be connected to a separate water pump , so you will not have to disrupt the filter hose to install it - as seen from the green pipes in the picture.)

Ködös víz (Cloudy Water)



White Fungus

This is a regular guest in new aquariums that have Red Moor wood in them. It always (!) appears on the wood in the form of white slimy surface - forming spots or continuous mold. It is absolutely harmless and it will disappear by itself after 1 or 2 weeks. The appearance of the fungus is caused by organic material and spores present in this type of wood. It's appearance is inevitable and we just have to wait until it disappears as it will not release harmful substances in the water. Some algae eaters will even eat it. If you do not like the look of it and would not want to wait to disappear, you can brush it off with a toothbrush.

In old tanks, fungus can be found in two places: on fish carcasses and rotting food. Physical removal (sucking out or taking it out with a pinsette) of these will solve the problem.

Fehér penészgomba

Other Issues


Brown Water or Yellow-Colored Water

Water can be colored by a number of reasons. Hardscape is the number one reason behind the brown water. Driftwood can release tannins, that will give the water some tint. Dark Iron Wood and Mangrove Roots are premier sources of color - even for longer periods (years). We can often see dark-colored brown waters in the nature, they even serve as natural habitat for certain fish-types that thrive better in waters like these - remember the Amazonas waters? Green Aqua offers certain products - like ADA Black Water, that explicitly have the purpose of producing these conditions.

If you are not happy with this coloring you can improve it with regular and larger water changes but you will need a lot of patience until most of the tannins have been released in the water from your wood. Using larger amounts of Seachem Purigen in your filter will drastically improve the transparency of aquarium water - you will get crystal-clear view within hours. The absorbing capacity of Purigen is limited, so you might have to recycle or change it after some time.

You would be amazed to find out that lower quality aquarium glass (not opti-white glass) can also cause the water look a little brownish. Try to have a highly transparent, clear, opti-white glass aquarium if possible.

Barnás árnyalatú víz

Bad Smell

In contrary to the smell of older "conventional" fish tanks, the modern Nature Aquarium should not have any smell at all. The crystal-clear water and harmony of living creatures within should create an eco-system that releases no gases. If your Nature Aquarium smells, it is because there is some problem with the system and gases are being released in the air through the water surface.

The traditional "aquarium smell" (marsh smell) is mainly coming from Ammonia gas - formed as a result of organic decomposition. Ammonia, in higher concentrations smells like urine. These smells will indicate general hygiene problems: the gravel is not clean (wrong type of substrate), the filter is not clean, the system is not designed well (you have week filtration), plants are decomposing because of the lack of CO2 and/or nutrients, you do not change your water and clean your aquarium regularly, etc.

If your aquarium smells, you need to clean it thoroughly, clean the filter, make a bigger water change and create conditions under which the nitrifying bacteria can do their job, transform Ammonia into Nitrate. If there is irreversible rotting in the substrate you might even have to take your aquarium apart and start over with a new ecosystem, replacing the substrate.


Cloudy Water - Bacterial Bloom

If the water cloudiness is caused by bacteria, adding more filtering bacteria will not help the issue. Also, stronger filtration or frequent water changes will most likely proove useless. You could try to use Seachem Clairy. If the problem comes back, you might want to add some Activated Carbon to the filter media. If that will not solve it, you'll have to intall a UV filter.


Foamy Water Surface

The foamy water surface is a type of Surface Scum (discussed above). The protein layer on the top of your water is filled with bacteria and this forms a "cap" on your aquarium not letting the gasses to escape - so they will accumulate under this layer and form bubbles, producing a foam at the end. Please refer to the Surface Scum description for further details.

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