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Algae and moss are tiny organisms that can cause significant problems in aquariums. Not only do they detract from the natural beauty of your tank, but they can also affect the health of the creatures living inside. To maintain a beautiful and healthy aquarium, it's crucial to understand the different types of algae and moss, as well as how to prevent and control them.

Green spot algae (GSA)

There is a difference between green spot algae (GSA) vs green dust algae (GDA). Green spot algae forms distinct circular dots that are very tough to scrape off while green dust algae is easily wiped/scrapped away though it may form a thick layer that is harder to clear. Spots usually take longer to form, while green dust algae can form a green film across the glass within a day or two. Commonly strikes old growth first.

If this is the only algae present in the planted tank, and you are not dosing phosphates at all, it may indicate plants are not receiving enough phosphates.

Having slow growing plants (Anubias, Buceps) in bright light doesn't guarantee that they'll get green spot algae- as long as you can solve the underlying issues in the tank, they can be clean.

Nerite snails do eat GSA & GDA albeit slowly. Shrimps pick on both. Livestock alone are seldom adequate to solve issues though - algae multiples at a much faster rate when the root causes are not solved.

Common Causes

Quite frequently, carbon (CO2) and macronutrient (NPK) deficiencies are the reason for the formation of algae. In the following list you can find the favorable values for the individual nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)

Solutions

​Prune off old/dead growth, replant new tips
Address plant health issues
Spot-dose APT Fix
Clear organic detritus in planted tank

If you notice an increasing population of spot algae in a planted tank, we recommend you delve a little deeper into the subject of phosphate fertilisation. You'll need a special water test to determine the phosphate content of your aquarium water. Usually, spot algae appear if the phosphate content is too low or too high. If the phosphate reading shows that the level is too low (at the lower detectability threshold) you can easily add this nutrient with the corresponding fertiliser.
However, if the phosphate content is much too high (at around 3 mg/l or above), you'll need to remove some of it by large water changes or by using a phosphate binding filter medium for a bit. If you are adding phosphate with a fertiliser you'll need to reduce the dosage in accordance with the values you measure. Generally, regular water changes are important to prevent nutrient buildup. We recommend you change around 50% of the aquarium water per week.

After adjusting the phosphate content of the water, remove the spot algae from the glass. This will enable you to monitor the formation of new spot algae. Ideally the algae has been stopped, though, or at least is under control.

Cyanobacteria (Blue green algae)

Biologically speaking, blue-green algae are no algae but bacteria. In contrast to all algae, these cyanobacteria (also called blue bacteria) do not have a true nucleus, however, just like plants, they can photosynthesize. There are many different types of BGA, some float in the water (e.g. some species in the genus Microcystis) or some that form gelatinous lumps on wet ground (Nostoc). However, in the aquarium hobby we know cyanobacteria as dark green, blue-green to almost black coats on aquatic plants, decoration or the substrate. They feel slimy to the touch and are thus sometimes called slime algae. Their unique pungent smell is characteristic - the odor can be described as "foul" or "earthen". Quite often, slime algae belong to the genus Oscillatoria (filamentous cyanobacteria). Small populations, for example on the fringe between the substrate and the front glass, are quite normal and no reason to fret.

Cyanobacteria, or blue-green algae (BGA) appears as dark green slime. This algae starts as translucent sheets, often along the substrate, and hugging poorly growing plants. It can form filaments that trail in the current. It is often caused by a combination of deteriorating plants, excess organic waste at substrate level, poor oxygen levels, and low nitrates. BGA is actually a photosynthetic bacteria capable of fixing gaseous nitrogen. In large amounts, it smothers plants and plant growth can stall - giving rise to more issues.

Algae eaters often avoid this algae as it can be toxic.

Common Causes

As with true algae, a nutrient imbalance may be the reason for an outbreak of cyanobacteria in a planted aquarium. In various cases, the reason was a highly elevated phosphate level, sometimes in combination with a nitrogen deficiency (more specifically, a nitrate deficiency).

On the one hand, a regular water change is thus highly important to prevent this kind of nutrient spikes. We recommend to exchange around 50% of the aquarium volume per week. On the other hand, in a planted tank a balanced nutrient supply is crucial for the healthy development of the plants. Quite frequently, carbon (CO2) and macronutrient (NPK) deficiencies are the reason for the formation of algae. In the following list you can find the target values for the individual nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)

Blue-green algae are bacteria, and one of the reasons for a BGA infestation may lie in a disturbance in the balance of the so-called microflora. This term applies to all the bacteria and microorganisms in the biofilms of the aquarium. If these other microorganisms are present in insufficient numbers or if there is an imbalance of them and cyanobacteria, BGA may increase their numbers significantly as they lack competitors for nutrients. This phenomenon occurs most frequently during the cycling phase of a tank, as the biological system is still finding its balance. In this case you ought to add beneficial bacteria to your tank, for example by using preparations containing these bacteria, like Special Blend and Nite-Out II. It may also be helpful to add some muck or filter sludge from another aquarium that is biologically stable.

Solutions

Small spots can be manually removed or spot dosed with APT Fix.
Improving circulation & oxygenation in affected areas can clear mild cases
Serious outbreaks may require anti-biotics; Erythromycin. This may impact your nitrifying bacteria though. Commercial products such as UltraLife Blue green slime remover and Chemiclean works as well.
Serious outbreaks may be solved by 3-5 day blackout.
Water changes and light substrate vacuum to clear organic debris.
Increase dosage of nitrates if plants are nitrogen starved.

Green dust algae

Green dust algae forms a green film on rocks and most noticeably on walls of planted tanks. It is easily wiped off but comes back quickly. In tanks with strong light it can reappear within a day. In less severe cases, it means weekly scraping/wiping of tank walls. For aquascapers that only have had tanks that suffer from chronic GDA, wiping the glass on a weekly basis might seem like an inevitable thing - we assure you that it is not. GDA is differentiated from GSA (Green spot algae) easily as it grows much more quickly (with no particular dot formation) - and forms an obvious thin green film on tank walls.

GDA is more common in "hot" tanks - tanks that have tons of lighting and nitrogenous waste. Ammonia or nitrogenous waste can trigger it easily. Tanks with high NO3 levels (above 10ppm) and not enough plant mass are also very vulnerable to it. Many EI based tanks suffer from this. Cooler tanks, with more moderate lighting, leaner dosing regimes have much less issues with this.

Common Causes

Apparently, a massive appearance of this algae is caused by radical changes in an aquascape or planted tank, like for example drastic changes in the light, the technical equipment or the plant mass (e.g. after a severe trimming session). Some aquarium keepers have made the experience that large nitrogen peaks, caused by magnesium nitrate or urea, can trigger a GDA infestation. Please make sure you change water on a regular basis (at least 50% of the tank volume per week), not only to add fresh water but to prevent nutrients from accumulating. 

It is also important to adapt the amount of nutrients to the actual requirements of your aquarium plants. Especially when it comes to carbon (supplied through CO2) and macronutrients (NPK), imbalances in the nutrient supply may cause algae growth. In the following list you can find the favorable values for the individual nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)

Biologically immature tanks
Lack of dominant plant mass in tank
High light coupled with heavy water column fertilization (Common in tanks with high NO3 > 10ppm), warm temperatures
Organic detritus build-up in tank (watch the vid on water changes)
Poor oxygen levels in tanks

Solutions

If you have a problem with green dust algae you should try just sitting it out. Do not remove the algae layers but wait at least three to four weeks without doing anything. As a rule, the life cycle of these algae is over then, and the coats get incoherent. Algivores like some snail species and suckermouth plecs will eat them.

Alternatively, you can lower the water level in your tank as far as possible after the life cycle of the algae has ended and then wipe the remains of the algae off the glass. Do not remove the coat during the waiting period of three to four weeks, as the algae will release spores which start a new life cycle as soon as they settle.

Build up dominant plant mass in the tank (70% + planted)
Optimize CO2 levels (>30ppm)
For mild cases, APT Fix will work
3-5 days blackout for serious cases
Consider a leaner dosing regime (specifically, lower NO3 levels - keep it at 5ppm & below, till things stabilize. This is specific for EI fans for which this seems to be a common problem)
Lower water temperatures help significantly (<24 degrees celsius)
Better oxygenation helps

Green water algae

This form of algae is also known as "green pea" soup. The water turns into a cloudy green colour. 

Green water is caused by microscopical green algae that turn the water green. Within a few days they can inhibit the visibility under water significantly. These green algae usually are in the genera ChlorellaAnkistrodesmus and Scenedesmus, however, there are more floating algae from other groups, like e. g. the flagellate protists from the genus Euglena). In natural waters, floating algae are part of the so-called phytoplankton, they are important food for filter-feeding animals like daphnia, mussels and mysid shrimp. Sometimes, green water is the result of a whitish discoloration of the water. These algae float freely in the water and do not settle on surfaces like the glass, decoration or equipment in the tank.

Common Cause

The primary cause is excess ammonia coupled with strong light for extended periods. This may occur particularly in new tanks / planted tanks that are not biologically mature. It often results from over-feeding, high levels of livestock waste and/or plant decomposition. It is more common in very warm tanks (80f+).

The reasons for a sudden floating algae outbreak can for example lie in seasonal changes like an increase of the temperature during spring and summer or strong sunlight.

In a planted tank or an aquascape, which are fertilized, often nutrient imbalances are the root of an algae problem. Especially in the field of carbon (supplied with CO2) and the macronutrients (NPK), a balanced supply is crucial for the aquatic plants. In the following list you can find the target values for these nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)

To prevent unwanted substances from building up, change water regularly. We recommend a weekly water change of 50% of the aquarium volume. Refill the tank with fresh water.

Often, algae blooms occur during the cycling phase of a newly set-up tank. As the young biological system in such a tank is still finding its balance, algae can make use of that situation, and spread considerably. If the new tank has been planted well, and if the aquatic plants in there get sufficient nutrients, it is only a question of time until the algae are outcompeted by the plants.

Solutions

If you have problems with green water, we can recommend the use of a UVC purification unit. To work as efficiently as possible the unit needs to be connected to a separate pump with a low flow rate. If you connect it to the external filter, the water flow is usually quite high. However, the UV rays work better and kill more of the floating algae in the water if the contact time is as long as possible. After a few days, the algae bloom ought to let up. Change as much water as possible to remove most of the dead algae and to prevent them from polluting the water. Disconnect the UVC purification unit . You should not run it permanently in a planted tank, as it may have a negative effect on the complexing agents used in some fertilisers for aquatic plants.

Some mild cases disappear on their own as the tank matures
Immediately lower light intensity (by increasing the distance of the light source from the tank or adding shades) and reduce lighting-period to 5 hours until problem disappears
Mild cases can be cured by over-dosing APT Fix(with care) or by using Purigen as filtration media
4 - 5 day blackout for serious cases
Use Diatom filters
UV steriliser is a 100% cure for serious cases

Cladophora algae

Cladophora appears as tough filaments or green turfs in areas of high light and poor flow. They are tougher than ordinary types of 'hair' algae and do not break apart as easily as other filamentous green algae. They can be identified by their  distinctive smell. This is a higher level algae that is not deterred by healthy plant mass - although larger, more robust plants will out-compete it by shading it out. Mosses and fine carpets, and slower growing plants are more vulnerable as a whole. Over-crowded areas with old growth are also vulnerable.

Common Causes

Slow flow, high light dead spots
Slow growing, over-crowded spots
Decaying undergrowth

Solutions

Manual removal, spot treat with FIXLITE.
Prune / remove old growth.
Increase growth rates by optimizing CO2, nutrient levels.
Reconfigure problem areas to feature larger, more robust plants.

Staghorn algae

Staghorn algae (Compsopogon sp.) belong to the group of red algae. They are easy to diagnose as their growth habit looks a bit like the horns of a stag. They show different shades of grey. If you immerse a piece of these algae in alcohol it will assume a red color. Staghorn algae are usually found on aquarium decoration, technical equipment and the margins of the leaves of aquatic plants. They are hard to remove manually. These algae seem to be quite unattractive for most algae-eating aquarium animals.

Staghorn algae appear as thick grey hairs on the edges of leaf margins. They can be hard to remove by hand. They differ from BBA (Black brush algae) in that BBA has a finer texture and usually darker color.

They can be triggered by tank instabilities that cause plants to be stressed - such unstable CO2 levels or irregular fertilization or a spike in ammonia/organic waste levels such as skipping water changes in a tank that has previously been on a stricter water change schedule.

Staghorn algae is commonly found attached to the edges of slow growing plants.

Common reasons

In planted tanks that are supplied with liquid fertilisers the appearance of these algae is often an indicator for an overdose of the iron fertiliser. Please adjust the amount you give and reduce it. If you have a water test for iron at hand, check the amount of iron dissolved in the water. Aim for 0.05 to 0.1 mg/l of iron (Fe). If the test has higher reading over a longer period of time this means that the fertiliser is overdosed. The iron content should not be permanently measurable if you use weakly chelated iron fertilisers like the Aqua Rebell Spezial Flowgrow. The nutrients contained in these fertilisers are taken up by the plants very rapidly and thus disappear from the water very soon after the addition. As long as your aquatic plans do not show any signs of deficiencies (like white shoot tips) you may reduce the amount of fertiliser you add step by step.

Furthermore, the plants should be supplied with ample amounts of CO2 and macronutrients (NPK) in a balanced way. If one of this elements is in undersupply, the growth of the plants is limited, according to the Liebig minimum law, and the unused nutrients like iron and trace elements can accumulate. It is possible that such an imbalanced nutrient supply is responsible for the increased growth of red algae like staghorn and brush or beard algae. In the following you can find a list of target values for each plant nutrient:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)
As nutrient imbalances may result from lax maintenance we'd like to point to the importance of regular water changes. We recommend you change around 50% of the aquarium volume per week. This prevents the accumulation of nutrients and other substances.

Spike in ammonia/organic waste levels
Stressed plants/old growth
Change in tank regime that causes temporary instabilities

Controlling staghorn algae

You have run into problems with staghorn algae in your aquarium? We recommend the addition of Easy Carbo. According to the manufacturer, you can add 1 to 2 ml of this product per 50 l of aquarium water. After a few days, the staghorn algae will turn a white or pink color. If they show this discoloration, you can stop the treatment. The dead algae are eaten by shrimp and other aquarium inhabitants.

Have a regular maintenance/water change schedule
Have a regular fertilization schedule and stable CO2
Pruning and replanting of healthy tops, discard old growth
Spot-dose with APT Fix directly on algae
Don't panic - it may be temporary and will pass

Fuzz/hair/thread algae (Filamentous algae)

While there are various types of filamentous algae types, they all have similar base causes & triggers. The common trigger is a spike in organic waste/ammonia. This may occur due to heavy usage of ammonia/urea rich fertilizer. (such as burying root tabs not deep enough). Dead livestock, poorly functioning filters, damaged or stressed plants can all be sources of ammonia. High light is an accelerator but by itself alone seldom trigger filamentous algae.   

If found growing on or attached to even fast growing stem plants - this generally means that plants are either damaged, stressed or deficient. 

When algae preferentially attaches to plants rather than hardscape, it happens because plants have deteriorating leaves ( due to age/nutrient deficiencies/damage ) or are under stress (transplant stress/pruning/unstable parameters etc). Plants under harsh/fluctuating conditions continually re-program their enzymes to try to adapt to new conditions - older DNA is ejected from the leaves as organic waste & ammonia. This becomes a chemical signal for algae to attach opportunistically; the deteriorating leaves feed algae by releasing carbohydrates and sugars; if the plant is not dosing well it means that the algae will not be shaded over by new growth. This is how simple chemical triggers can allow algae to compete against higher level plants. In such situations, stabilizing the tank and improving plant health is critical.

Healthy, well maintained planted tanks should be completely free of filamentous algae. 

Plants can show signs of growth even under stress - an unstable tank can still show regular plant growth. Signs of stress include; algae on leaves, premature shedding of older leaves (bare lower stems), uneven leaf sizes/shapes/coloration, stunted growth tips, elongated inter-nodes, thin/brittle stems & leaves.

When left unattended, deteriorating leaves combined with high light levels can result in algae ( thread / hair algae above, for instance) taking over a tank completely. 

General Causes

Unhealthy, deficient, or stressed plants (sub-optimal CO2, nutrient issues, overcrowding, transplant shock, physical damage, over-pruning stress, unstable or extreme tank parameters).
Abundance of old, deteriorating growth.
Spike in Ammonia/urea source in tank. (terrestrial osmocote, uncycled tanks, heavy feeding, nutrient formulas that contain Urea/Ammonia, dead livestock)

Solutions

Replant healthy tops and discard old bottoms - keep doing this till no more visible algae attachment to old growth. Prune off badly affected old growth
Mild cases would generally disappear by themselves as plant health and tank stability improves.
Severe cases can be killed off by APT Fix & other commercial algicides but base causes need to be addressed or the algae may return.
Solve underlying plant health issues - this algae rarely occurs naturally without a trigger.
Water changes, clearing of detritus, old growth.
Plant larger, more robust, easier plants to increase plant mass in the tank.

Fuzz algae

The term "fuzz algae" describes short green algae growing as individual filaments on plants, the decoration and even the aquarium glass. They are easily confused with hair algae. Those, however, do not grow in individual filaments but form a dense coat on objects. The filaments grow much more densely than those of fuzz algae. It is still unclear whether fuzz algae are an early growth stage of a hair algae species, though.

Common causes

Fuzz algae are a clear sign of an imbalance in a young ecological system. They are frequently found in aquaria that have been existing for a short time only, approximately during weeks 4 through 8. A sudden outbreak of fuzz algae in an older set-up is often caused by imbalances of the macronutrients (NPK). A permanent but slight population of fuzz algae is quite normal and no reason for concern.

Control

Optimising the nutrient supply leads to improved plant growth. Fuzz algae are then easily outcompeted. Aquatic plants rely on a balanced nutrient supply. Which conditions and nutrients they need in the aquarium has been laid down in this article about aquarium basics. Quite frequently, fuzz algae appear when there is a carbon deficiency (remedied by adding CO2) and a deficiency of macronutrients (NPK). Please look up the target values for these nutrients in the following list:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)
The algae should face competition by a sufficiently large, healthy, fast-growing aquatic plants. Given that the nutrient supply is well-balanced, adding more plants can be helpful to fight fuzz algae.

Using a sufficient number of algivorous aquatic animals is highly recommendable. Amano shrimp (Caridina multidentata, also known under their old scientific name C. japonica) are excellent algae-eaters, as are some dwarf shrimp species like Neocaridina davidi or Caridina logemanni.

Hair algae

Hair algae are quite commonly found green algae. They form coats, from which densely packed short filaments grow. They form carpet-like layers, growing over plants and decoration. These algae usually belong to the genus Oedogonium. The species in this genus differ by the length and build of their filaments. Hair algae with longer, soft filaments are frequently found in aquaria.

Common causes

Like many green algae, hair algae appear mainly during the cycling phase of a tank, when the biological system is still finding its balance. After some more time, when the nutrients are optimally balanced and when a sufficient number of algae-eating aquarium animals is present, hair algae will disappear all by themselves. Algae with softer filaments are eaten by invertebrates like Amano shrimp and most dwarf shrimp species. Even snails like the highly popular ramshorn snails will go after the filamentous hair algae coats. There is one species with short, hard, bristle-like filaments (see photo), which is not commonly found but very stubborn.

Like green thread algae, hair algae can appear due to a nutrient imbalance, for example when some nutrients or CO2 are deficient. However, overly long lighting hours or too intense a light above the tank can be a reason for their occurrence. It is important to give the algae lots of competition on the form of a large number of fast-growing aquarium plants. For them to grow healthily and happily, a balanced supply of nutrients is vital, especially when it comes to macronutrients (NPK). In the following you'll find a list of these nutritive elements and the recommended content in the water. Using a CO2 injection system in combination with liquid fertilisers facilitates supplying your aquatic plants with everything they need very much.

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)
In the following, we'd like to explain the most common causes for green algae in more detail:

CO2

The content of dissolved CO2 in the aquarium water is best monitored with a permanent test filled with test agent. Renew the test agent every four to six weeks so your permanent test always works reliably. The ideal concentration of CO2 is at around 20 to 30 mg/l, which is indicated by the color green inside the permanent test.

Light

If the light is too strong in relation to the requirements of the plants and the nutrient supply, hair algae may occur. When you switch to another light system or leave on your light for a longer time, always adapt your plant mass and your fertilisation regime. It is very important that the light requirements of the aquatic plants are in accordance with the lighting system. Most nurseries have a traffic light system to categorize their plants (green - undemanding, yellow - moderate, red - demanding). This is also a hint towards how much light a plant needs.
Moreover, we recommend keeping the daily lighting period in a newly set-up tank rather short, like only 6 hours, in the early stages. Increase by 30 minutes every week. If your light has a moderate to strong output, leave it on for a maximum of 10 hours per day. Tanks with weak light can be lit for up to 12 hours. You don't know just how strong your aquarium light is? Find out with our light calculator.

Nitrate

Often stunted growth in aquatic plants is due to a lack of nitrogen. This can be diagnosed by testing the water with the appropriate water test for nitrate. When the plants stop growing, especially green algae soon take advantage of this situation and use the nutrient imbalance to take over the tank. With good liquid fertilisers like for example Aqua Rebell Makro Spezial N or Advanced GH Boost N you can boost the nitrate (NO3) content in a targeted way. Other macronutrients like potassium or phosphate are not added by these fertilisers. If there is a lack of nitrate in your tank you can raise the content to the optimal level by a one-time stock fertilisation with Advanced GH Boost N. Combined with this measure you ought to adjust your regular fertilisation regime, be it weekly or daily, with a nitrate-only fertiliser.

Nutrient imbalances are often caused by a slack-off in maintenance. Please note: a regular water change is vital! Exchange at least 50% of the aquarium water for fresh water once a week. Besides the addition of fresh, unpolluted water a regular water change prevents certain nutrients from building up in your tank.

Control

As we've already said above: The typical countermeasures that are used against green algae in general also help against hair algae: the use of a sufficient number of algae eaters (for example Amano shrimp) hand in hand with an optimization of the fertiliser regimen, especially in the area of macronutrients (NPK). Is your tank still cycling? Then stay calm, it is absolutely normal that algae appear during this phase. When your aquarium has been running for a longer time, the ecosystem will become more and more stable, and the water plants will be able to outcompete the algae. If only a few leaves are infested, just cut them off and throw them away.

If the hair algae only grow in a few spots in your tank, try fogging them, preferably with hydrogen peroxide or in combination with Easy Carbo (Please note: do not mix these products, but use at different times). Easy Carbo as a single ingredient is not always efficient enough in the case of hair algae.

Is your tank more heavily infested with hair algae? Try a black-out treatment to get rid of them.

Thread algae

Typically, filamentous algae consists of long green threads that often feel rather soft and loose. Some of them break down if you try parting a tuft. They belong to different algae species. Natural algivores like the Amano shrimp just love eating this algae type. Filamentous algae do not attach themselves to the substrate, anchoring themselves with holdfast organs but form rather bushy cushions. In a strong current, individual filaments float in the water and get caught in decoration or plants, this is how filamentous algae spread.

Common causes

Quite frequently this type of algae is seen in planted aquaria that are just cycling. During the first weeks, the microbiology of recently set-up tanks is still quite unbalanced. The longer the tank has been running, the more stable the ecological system becomes. In the beginning, the balance between algae and higher plants is not quite established either. Bit by bit the higher plants will get the upper hand as they grow and as the plant mass in the tank increases. It is thus very important to have an ample amount of plants in a new tank from the beginning. Especially fast-growing stem plants are really great for keeping the algae in check. The plants need to be supplied with the full range of nutrients, with liquid fertiliser and carbon (CO2). In the following list you can find the target values for the individual nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)
Use only one third of the dosage recommended on the label of the iron fertiliser.
In the beginning, the tank is lit only 6 hours per day. Increase the lighting time by 30 minutes per week. If you have medium to strong aquarium lights, we recommend 8 to 10 hours of lighting time as target. If the lights are less strong you can leave them on for 10 to 12 hours per day. Our light calculator helps you determine whether your light is weak, medium or strong.

A sudden algae outbreak in a planted tank may be due to a nutrient imbalance. Quite frequently, a nitrate or CO2 deficit are at the root of the problem, or an increased light intensity (when you have installed a new light source above your tank), daylight or overly long lighting phases.

Let us go into more detail on the most frequent causes for filamentous algae:

CO2

The CO2 content of the water should be controlled with a permanent test and test reagent. Does the indicator inside the permanent test work correctly? Replace it every four to six weeks to ensure that the test reagent shows the right color. Ideally, the content of CO2 ought to be around 20 to 30 mg/l, to which the indicator reacts with a green hue.

Light

Too much light in relation to the plant mass may be the cause of an outbreak of filamentous algae. Did you exchange your fluorescent tubes or did you switch to another lighting system? If you increase the light intensity you always need to increase the nutrient supply, too. The light intensity needs to correspond to the requirements of the plants. If you need to exchange your fluorescent tubes, do this one tube at a time.
Does the aquarium get more daylight due to relocation or because the position of the sun has shifted seasonally? This might be another cause of filamentous algae.
Under moderate to strong light, the lighting phase of the tank should not be longer than 10 hours max. For aquaria with lower light, the maximum length of the lighting phase is at around 12 hours.

Nitrate

Quite often the plants will stop growing when they do not have sufficient nitrogen at their disposal. Nitrogen can be measured in the form of nitrate. Stagnant growth of the plants often enables the algae to take over. The nitrate content (NO3) can be measured with a water test. The target values for this nutrient are at around 10 to 25 mg/l. With a liquid fertiliser like Aqua Rebell Makro Spezial N or Advanced GH Boost N, the nitrate content of the water can be increased directly without strongly elevating other nutrients like potassium or phosphate. Bring the nitrate content to a higher level by moderately giving a single dose of Advanced GH Boost N to create a nitrate reserve. To maintain the nutrients at the desired level, adjust your fertilisation regime correspondingly; use a nitrate-only fertiliser if necessary.

As nutrient imbalances may be created due to a slack of aquarium maintenance, we'd like point out that a regular water change is vital. We recommend exchanging at least 50% of the aquarium volume per week to prevent the buildup of substances in the water.

Algae control

You have problems with filamentous algae? Here we give you an array of possibilities to regain control.

At first it is important to have a sufficient number of algivores in your aquarium. Invertebrates like Amano shrimp or dwarf shrimp (like Red Bee or Red Fire shrimp) will help you keep this algae type in check.

Stocking up on algivores temporarily is a good solution especially if you have several tanks. We recommend using a significantly larger number of these animals when algae appear during the cycling phase of the tank. When the tank has gained its biological balance, usually there is also a better balance between the algae and the higher plants. Then you can reduce the number of algivores and put them into another aquarium.

Does the tank have a low number of plants or are the plants slow growers? In this case we recommend you to stock up on healthy and possibly fast-growing water plants. This measure makes a lot of sense especially when your original plants are weakened by the algae infestation.

Are the algae only in a few places in your tank? You can remove filamentous algae quite easily by simply winding them onto a skewer with a rough surface. Some of the nests can even be siphoned out during a water change. If the algae keep reappearing in the same places even though you keep removing them, try fogging them with algicides like Easy Carbo or hydrogen peroxide.

Is the aquarium overgrown with filamentous algae? A black-out treatment is a rather easy and non-invasive way of reducing algae in an aquarium.

If none of these measures take effect, your last resort is a treatment of the entire tank, with an algicide like for example AlgExit or a treatment with hydrogen peroxide. Many planted tank keepers have had positive results with algicides. However, please keep in mind that using them for a longer period of time may have a negative effect on the microbiological balance, severely upsetting it. These remedies may also do damage to some aquarium plants or hinder their growth significantly. Some aquarium animals will die when exposed to AlgExit, like for example all nerites. Treating the entire tank with an algicide should therefore always be your last resort.

Black Beard Algae (BBA)

The term Black Beard Algae (BBA) refers to algae from the genera Audouinella, which contains many sub-species. Audouinella species occur in both marine and freshwater. These algae appear as short reddish or black turfs of hair. They grow in small bunches and first appear as small furry black dots as small as the tip of a pen. They are often found on the edges of older leaves of plants, or on hardscape and filter outlets. Some species can grow to more than a centimeter in length.

Why does BBA attach especially readily to plant leaf edges?

While they appear still and unmoving on the outside, there is complex biochemistry on going inside the plant as the plant generates carbohydrates, sugars and other metabolites from photosynthesis. Plants are leaky organisms and aquatic plants eject a portion of excess metabolites directly through their leaf surfaces and margins. Algae feed off these waste organics. When plants are under stress, for example, when adapting to a new environment, which requires a significant amount of re-programming of proteins and enzymes, the excretion of waste proteins and metabolites is increased. The plant becomes particularly vulnerable to algae. On the flip side, when plants are healthy, they generate defensive antimicrobial chemicals and enzymes to ward off pathogens and algae.

Stressed/unhealthy plants are thus algae magnets while healthy plants are very resistant towards algae. Older leaves leak more organics, and plants defend older leaves less as they are less valuable. This is why in most tanks, you see algae attaching only onto some plants but not others, and most commonly to older leaves first. Plant stress can be caused by many factors. Recently transplanted plants tend to face some adaptation stress as they adapt to the new environment. Insufficient CO2 or nutrient levels can cause poor growth as well. Frequently moving plants and making large changes to the tank environment are both actions that can cause plant stress as they try to catch up to the environmental changes.

In a tank where there is a lot of old deteriorating old leaves on plants, the environment is especially conducive for algae. In a tank where there is dominant plant mass and the plants are growing robustly with fresh new leaves, algae will find it difficult to survive. Thus, plant husbandry plants a big role in managing algae. Cutting off old leaves to make space for new growth, and replanting healthy tops/discarding old deteriorating bottoms are tasks that should be done regularly to maximize growth of new fresh leaves.

This approach of rejuvenating growth to avoid algae applies to BBA but is a universal concept that can be applied to manage all algae.

Black beard algae

Black beard algae (BBA) or brush algae (Audouinella sp., Rhodochorton sp.) belong to the group of red algae, just like staghorn algae. Their natural color is not red, though, but varies from dark green over grey to a deep black. However, if you put these algae in alcohol, they will turn reddish. This is an easy proof that the algae you're dealing with are actually red algae. Beard algae cling stubbornly to the ground they grow on, like technical equipment, the leaf margins of aquatic plants, aquarium decoration or even grains of the substrate. The algae tufts look like a beard or a brush, and that's where the name comes from.

High levels of organic waste & detritus in the planted tank encourages BBA to spawn. If they are found attached to plants, it is most commonly caused by stress induced by fluctuating CO2 levels. In tanks where plants are healthy, but there a high level of organic waste in the tank environment, BBA will be found attached to hardscape instead. 

If found on hardscape or driftwood, it is almost always found in fast flow areas in the path of CO2. Often this is due to aquarists obsessed with overly strong flow. It's commonly found on filter outflows, and on CO2 diffusers - which are often placed in the path of high flow. In such tanks, slowly down the flow or redirecting it to have more even flow distribution has a big impact.

Barr report suggests that BBA strives when CO2 is present but at low levels; between 10-15ppm. Non injected tanks (low tech tanks) and tanks with higher levels of CO2 are less vulnerable - to this end, it seems to occur most often in tanks where CO2 injection is used but optimized poorly.

Black brush algae has little connection to nutrient levels or light spectrum. Both tanks with very lean water column fertilization and rich water column fertilization are vulnerable to it. It has very strong correlation to organic waste levels, plant husbandry and CO2 fluctuations.

American flagfish, mollies and SAE (Siamese algae eater) pick at it when there are no tasty alternatives. However, they are seldom adequate solutions.

What causes black beard algae in planted tanks?

Black Beard algae are found in fish tanks as well as in densely planted aquascapes, for different reasons, though. In tanks with a high stock of fish and almost plants or no plants at all, the black color variant is often seen. In these tanks, the reason for their appearance is a high organic water pollution, due to overfeeding in combination with few water changes. In many cases, the algae population in these aquaria grows exorbitantly if lots of muck has build up in the filter and in the substrate. Cleaning the filter and using a gravel cleaner for getting rid of the muck in the substrate ought to help.

Quite frequently, there is no CO2 system on such a tank. It is believed that the content of free carbon dioxide (CO2) in the water plays an important part for the appearance of red algae like beard algae. If there is a CO2 deficiency, these algae can take the carbon they require from hydrogen carbonate, and with much more ease than higher aquatic plants. They can separate the carbon from the hydrogen carbonate ion, thus creating hydroxide ions, which elevate the pH. In this process, the so-called biogenic decalcification takes place, limescale (calcium carbonate) precipitates, which is in turn used by the algae to fortify their cell walls. They become harder and more unattractive to algae eaters.

Especially in fish-only tanks where a lot of food is given - but really for all aquaria, come to think of it - regular maintenance work including a weekly water change are vital. If you slack off with the water changes, unwanted substances can build up in the water. We recommend rather large weekly changes of at least 50% of the tank water.

In aquascapes or planted tanks, a well-balanced nutrient supply is vital for the plants. In planted tanks, you often have beard algae when there is an imbalance of micronutrients (trace elements, especially iron). If you already use an iron fertiliser, you ought to reduce the dosage. Measure the iron content of the water with a water test. It ought to be at around 0.05 to 0.1 mg/l. Of course, carbon (CO2) and macronutrients (NPK) should be added, too. In the following list you can find the target values for the individual nutritional elements:

A CO2 content of approximately 20-30 mg/l, measurable by a permanent test with test agent
10 to 25 mg/l of nitrate (NO3)
5 to 10 mg/l of potassium (K)
0.1 to 1 mg/l of phosphate (PO4)
>10 mg/l of magnesium (Mg)
If you have black beard algae in your tank, and the plants show signs of an iron deficiency at the same time (the shoot tips are of a much lighter color than the rest), you might want to consider switching to a less intensely chelated iron fertiliser like for example Aqua Rebell Spezial Flowgrow. Sometimes, adding iron exclusively (without the other trace elements) has been successful. For daily fertilisation we recommend our Aqua Rebell Mikro Spezial Eisen. Only add the standard iron fertiliser with trace elements only once per week, and sparingly.

Fluctuating CO2 levels in the tank.
High amount of organic waste/dirty tank.
Stressed plants/old growth.
Instabilities that lead to plant stress; poor water quality, harsh use of biocides etc
Excessive flow with heavy misting (observe if BBA spawns in areas that are directly in path of flow), especially on slow growers/moss/hardscape.

How to get rid of blackbeard algae?

Spot dose APT Fix directly onto BBA at first appearance to prevent spreading. It is highly effective against BBA.
Pruning and replanting of healthy tops, cut away and discard old growth.
Find ways to even out excessive flow. In many tanks, slowing down flow alone can prevent BBA from triggering.
Find ways to stabilize CO2 levels. Generally speaking, higher injection rates create more stable CO2 levels, so increasing CO2 injection is generally recommended.
Regularly vacuum substrate surface while stirring up debris with turkey baster (see below) to reduce organic debris - this makes a big impact.

Brown algae (Diatoms)

Diatoms (a member of the algal class Bacillariophyceae) appear as yellow green or brown patches, and/or as stringy brown mass. Diatoms can be found in virtually every freshwater and saltwater body, and are one of the most ubiquitous algae in the world, making up a quarter of the world's biomass. Photosynthesis by diatoms in the oceans produce more than 25% of the world's oxygen. They can be found in small amounts on the surfaces of plant leaves and the substrate - and are found in virtually every aquarium, regardless of how clean a tank may look.

Diatoms multiply rapidly when conditions are right, doubling in just 24 hours, however, the life span of individual cells are short, usually less than a week. Diatoms construct cell walls out of silica, and this has lead some to draw the conclusion that it is due to silicates from sand or soil that causes diatoms to bloom. Studies have shown (Kilham, 1971), that the silicate levels required for diatoms to thrive in freshwater are very low and most freshwater systems are rich in silicates - so the total removal of silicates does not seem like a practical approach in controlling diatoms. Most tap water contain silicates, as does substrates such as sand or aquasoil.

In planted aquariums, diatoms are especially common in new setups in the first couple of weeks. Thankfully, diatoms tend to fade by themselves, even in planted tanks with no changes in Silicate levels, as the plants settles in and the tank becomes biologically matured over 3 to 4 weeks. Tank maturity and plant dominance are stronger contributing factors to a tank being free from visible diatoms rather than specific water parameters or silicate levels.

Why do new tanks suffer from Diatoms more readily? Some have suggested ammonia or metabolites from stressed, freshly planted plants as possible triggers, while others have claimed that elevated phosphorous levels can be a trigger. Ion-exchange resins that absorb the above seem to work in some cases, but not work in other cases; perhaps they can be used in tanks where there are persistent cases as a last ditch effort. As with most biological systems, the trigger factors for algae are complex and often tied to more than a couple of variables.

Diatoms reproduce very quickly, and many algicides are not particularly affective against them. Plant husbandry, and getting new plants adapted to the tank, does have a big impact on algae.

Common Causes

The appearance of diatoms during the cycling phase of a tank is absolutely normal, and you need not take any countermeasures. As a rule, the diatoms are crowded out by green algae a few weeks later in the life of your new tank, and they will not reappear.
Diatoms need silicate to grow, more exactly, silicon dioxide, since they construct their box-like cell walls from this substance. If you use tap water with high levels of silicate in your tank, diatoms have sufficient material to reproduce in a new tank. A lack of competitors like other algae and microorganisms will boost their reproduction rate.

Biologically immature planted tanks
Sustained presence often caused by tank instabilities that resets/disrupts the biological cycle (exotic substrates, especially for DIY dirt substrate users can face this)
Poor water quality from tap
Elevated ammonia or phosphorous levels in a biologically immatured tank

Solutions

As we have mentioned above, diatoms that have formed during the cycling phase of the tank will be outcrowded by other algae species bit by bit, especially by green algae. To keep their growth in check you can easily remove the brown layers, for example by siphoning them off with a hose. Many algae eaters just love to eat diatoms, too, amongst them all algae-eating snails and shrimp, as well as the different species of suckermouth plecs.

If you have a permanent diatom problem in your tank despite a sufficient number of algivores, you ought to check the silicate reading of your aquarium water with a water test. If it is too high there are several possibilities of lowering it and of thus taking away the main source of reproduction of the diatoms. You could use a reverse osmosis system to create water that only contains traces of silicates, or alternatively use special filter media that lower the silicate content in the aquarium water directly. Please keep in mind that these products will also significantly reduce the phosphate content of the water, which can have a negative effect on the plants.

Actions that help speed up tank cycling
Plant husbandry techniques to get plants adapted more quickly as described on this page
Manually siphon off mild cases
Ion-exchange resin that removes ammonia/phosphorous in desperate cases

Just as many papers show links between phosphates and algae. Concepts from surveying natural systems do not necessarily transfer directly onto how our aquariums work. Silicates are in most tap waters and soils; and most aquariums have no lack of them. A newly set up planted aquarium with low silicates from the tap water can still suffer from a diatoms outbreak. On the other end, a well planted, biologically matured aquarium will see no diatoms even with elevated Silicates or phosphorous levels. It is much more practical to focus on overall plant health and plant dominance in a planted tank.

Conclusion

Preventing and controlling algae and moss requires patience and persistence. By understanding the causes and implementing appropriate measures, you can create a healthy and beautiful aquarium.

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