Algae in the Aquarium

In addition to sudden fish death in the aquarium’s start-up phase and difficult-to-treat fish diseases, algae are probably one of the most significant sources of frustration for new (and experienced) aquarists. Although the mechanisms behind rampant algae growth are pretty easy to understand and remedy, you may require some patience, knowledge and fine-tuning to deal with algae problems.

What Is Algae?

All life on earth is divided into three different domains: eukaryotes, bacteria and archaea. In simple terms, they are distinguished by the structure of the cells. What is commonly called algae is not even in the same domain, taxonomically, as what was previously called blue-green algae (in freshwater) and are, in fact, cyanobacteria. 

There are hundreds of species of cyanobacteria, and, like “real algae,” they can photosynthesize.

Algae is a collective name for single—or multicellular—organisms that can perform photosynthesis, are usually found in water and do not multiply by forming seeds. 

Previously, all algae were considered to belong to a group of organisms that multiply by spores (cryptogams), but as genetic engineering, among other things, has developed, it has been realized that such a simple division is not accurate. Algae also contain different types of chlorophyll.

The domain of eukaryotes has traditionally been divided into four different kingdoms: animal kingdom, plant kingdom, fungi and protists. The latter are simple organisms that are “neither fungi, plants nor animals” and include, among other things, certain algae that are not considered to belong to the plant kingdom even though they look like a plant. 

Without going deeper into the more modern division and classification of different types of organisms, you can say that different algae benefit under different conditions, so it’s important to know their preferences to fight them.

Should I Remove Algae in the Aquarium?

Having algae in the aquarium is not in itself dangerous. In fact, you will always have algae in your aquarium because they are basically everywhere around us. However, you want to achieve a balance in the aquarium where light and various nutrients are at such a degree that the amount of algae is kept at a reasonable level. 

Some aquarists tolerate quite a lot of algae and think that it looks nice and natural with a little growth on rocks and roots while others absolutely do not want to see a hint of algae.

What Causes Algae Growth?

In general, we can say that algae growth is caused by an imbalance between nutrients in the aquarium water and the light or lighting in the aquarium. Algae can survive and multiply under conditions that are far worse than what an aquarium plant can handle. 

As long as there is light, algae growth can occur even if the supply of nutrients is minimal. Algae and plants compete for the same nutrients and light, so an excellent way to avoid algae growth is to make sure that your aquarium plants thrive as well as possible. That way, they can compete with the algae. 

The organic waste from the fish, leftover fish food, and plant parts that are broken down in the aquarium are, among other things, nitrates and ammonium that both plants and algae can use as nutrients.

This means that algae are likely to occur even in an aquarium without living plants because, by definition, it will always be out of balance. 

The fish release nutrients through the feces, leftover feed secretes ammonium, and the aquarium lighting provides the light needed for algae growth to take place. 

Since there are no plants in the aquarium that can assimilate the excess of nutrients, the growth will take the form of algae instead. Therefore, it is important to have a reasonable number of lighting hours, regular water changes and maintenance (and of course a good filter with great biological purification) in such an aquarium so you can “beat the problem before it starts,”, so to speak. The feeding should also be well balanced in relation to the number of fish in the aquarium.

brush algae

In an aquarium with living plants, water changes can have the opposite effect. Two substances that you usually want to get rid of through water changes are nitrate and phosphate. As previously mentioned, they function as plant nutrients, so when the water change is carried out, the nutrient levels fall and there are fluctuations in carbon dioxide content, oxygen content and other water values. 

Algae are opportunists and are quick to take advantage of these changes, while aquarium plants prefer stability. Therefore, it is better in a planted aquarium to make necessary water changes as infrequently as possible. 

With that said, you should make water changes of 30-50% every week if you already have algae problems or conditions that make algae easily formed.

The Quality of the Light Source Is Important

Algae are better than aquarium plants at utilizing the light available and can grow under lower luminous fluxes and more limited wavelengths. Therefore, if you have an aquarium with live plants, it can sometimes be better to increase the lighting or replace old fluorescent lamps than, for example, reduce the number of light hours. 

In the same type of aquarium, on the other hand, a large luminous flux means that the plants consume more nutrients and trace elements, which means that you may have to add nutrients to benefit the plants.

In addition to nutrients and light, the amount of CO2 also determines how well the aquarium plants thrive. Carbon dioxide is also something that disappears when you change water but can be replaced relatively quickly with carbon dioxide injection. 

The role that carbon dioxide plays in counteracting algae growth is thus partly to optimize the conditions for the aquarium’s plants, but also to restore water values ​​after a water change. 

This means that in a plant aquarium with good plant lighting, well-balanced fertilization of the aquarium plants and stable CO2 levels, you can make more regular and larger water changes than in an aquarium without the addition of carbon dioxide. In the same way that you should not overdo the supply of nutrients in your aquarium, you should not overdo the supply of CO2.

It is difficult, if not practically impossible, to get rid of algae by regulating the temperature in the aquarium. Different species of algae have different preferences when it comes to water temperature, but in general, we can say that you need to reach about 95° Fahrenheit or temperatures lower than 60° Fahrenheit for it to have a significant adverse effect on the algae. In most cases, your fish or aquarium plants will take more beating than the algae under such conditions.

uvc filter

Water hardness or pH value is also not a practical way to control algae. They generally prefer neutral to alkaline pH but tolerate a surprisingly wide range. For example, some microalgae are grown in very acidic environments with a pH of 0-5.5, and there are those that grow well in alkaline environments.

A UVC filter is a very effective tool for dealing with algae spores found in the water. Such a filter consists of a small pump that pumps the water past an encapsulated lamp that emits UVC light. This type of UV light is antibacterial, kills viruses and destroys genetic material in living organisms. 

Usually, you see results within a couple of days, and the method requires minimal effort. The disadvantage of a UVC filter is that algae attached to furnishings, glass and decorations are not affected and must be removed manually.

The easiest thing to do is simply lift out the contents of the tank that are easy to access and brush algae-occupied areas under lukewarm tap water. 

You can treat plants with a lot of algae on with scissors, or you simply pinch off leaves that have visible algae grips. You can brush stones with a small but powerful brush without removing them from the aquarium. 

The glass is easiest to clean with an algae scraper or algae magnet. Finish a major clean with a water change so that you do not have a lot of algae and other plant parts left in the water. The algae are otherwise broken down, releasing nutrients and consuming oxygen, creating good conditions for the next algae attack. Remember NOT to clean your filter at the same time, as you want to keep the beneficial bacteria.

Different Types of Algae

Diatoms (Bacillarlophycea)

Diatoms appear as brown coatings on plants, furnishings, aquarium accessories and aquarium glass and are sometimes called brown algae. This type of algae requires access to silicates and ammonium to thrive, which is often found in abundance in newly started aquariums. 

Before the nitrification bacteria have established themselves properly in the aquarium, there is nothing to take care of the ammonium added to the aquarium through the fish feed and the fish’s feces. The small amounts of silicates that the algae need are found in ordinary tap water.

Typically, diatoms will be corrected only by the regular maintenance of scraping the windows and brushing off the algae where you see them, and water changes. 

Eventually, they face competition from other algae and the nitrification bacteria and disappear—but you should also feed the fish more sparingly. Shrimp, snails, Ancistrus species and pleco like to eat diatoms, but if you have long-term problems with this type of algae, you can buy a water test and see how much silicate there is in your tap water. Should it show elevated levels, there are filter media that remove it.

Beard Algae

Beard algae most often occur on slow-growing aquarium plants such as anubias, or on rocks and roots in the aquarium. 

The most common cause is lack of maintenance and imbalance in the aquarium, so more frequent water changes and more thorough cleaning of the aquarium will probably reduce the problems in the long run. In addition, it may be time to review lighting, plant nutrition, and feeding schedule in planted aquariums to correct any imbalances.

Beard algae are stubborn and sit tight on furnishings and plants. It can be challenging to get rid of them with a stiff toothbrush, and if they are on stones, you may need to use a wire brush to remove them. Beard algae on plants are most easily removed by cutting or pinching off infected leaves or grooming bottom-covering aquarium plants with scissors. 

Real stones and roots can be placed in the oven for up to a couple of hours at a low temperature (160° F) if you do not want to use chemicals.

To treat an attack head-on, you can use some form of “liquid carbon,” such as EasyCarbo. This is done by lowering the water level in the aquarium so that you can brush or spray EasyCarbo directly on the algae (do not overdose) and let it work for up to a minute. The active substance is called glutaral, which effectively kills algae. Keep in mind, however, that this type of spot treatment does not address the underlying problem.


Phytoplankton is commonly called “green water.” This is because the aquarium water becomes green and cloudy, often with a view of only a few centimeters. The algae multiply quickly, and even if you make significant water changes, they will return within a few days. 

Using a UVC filter, you usually see excellent results within a couple of days, but, if you do not address the basic problem, it can reappear when/if you turn off the UVC filter. Therefore, before you connect the UV filter, make a complete water change and darken the aquarium for a period.

In the long term, you can plant more fast-growing plants or use floating plants that absorb the excess nutrients. Make sure that the sun does not shine directly on the aquarium. Sometimes a filter that is too small can be a contributing factor to getting phytoplankton in the aquarium.

Wire Algae

Thread algae is a type of algae that looks like green strands or hairs. They like strong lighting and are happy to take residence if nutritional values ​​or carbon dioxide levels vary a lot, such as using CO2 injection and unexpectedly running out of CO2. 

In addition to the usual routine when you get algae problems (water changes, better maintenance, balanced feeding, etc.), manual removal applies. Most people recommend using a toothbrush to remove the algae. 

Algae-eating fish such as Siamese algae-eaters are also usually very helpful in getting rid of this type of algae.

Siamese algae eater


Because cyanobacteria are not a plant but a bacterium, they do not react significantly to chemical pesticides against algae and weeds. If it is a significant infestation, one way to get rid of them is to obscure the aquarium for up to a week. 

The blackout must be total; no light must enter at all. While the aquarium is darkened, the fish are not fed. You may need to repeat the procedure if you do not get a satisfactory result on the first try.

Blackout can make the aquarium plants take a beating, and it does not really solve the fundamental problem. 

To prevent the cyanobacteria from returning in the long term, you should expand your maintenance routines with more frequent small water changes and sludge-suck the bottom substrate a little more often.

Algae Eaters

A common and good way to deal with algae is to get residents of the aquarium who eat algae. A few different snails, shrimp, catfish, and other fish are usually recommended in these contexts, and most people can probably find a species that suits their aquarium.

However, there is probably no algae eater who eats all types of algae, so you have to adapt to the kind of algae you have problems with or want to get rid of. There is also quite a difference in how much algae they can clean up.

Siamese Algae Eater

Siamese algae eater is one of the most popular fish to fight algae. They mainly eat algae when they are young, and they prefer to be in a group. Keep in mind that they will be pretty large, around six inches as adults, and then they need a large aquarium of 200 liters and up.


Ancistrus is a genus of freshwater catfish. The bristlenose catfish is a very popular aquarium fish that can be kept in most pet aquariums. They are hardy, easy to play and good algae eaters (especially as young people). In addition, they have a cool look! However, they get pretty large, so make sure you have a large enough aquarium.

Otocinclus Affinis

Otocinclus is a small catfish in the family Loricariidae. Since it is not as big as Ancistrus, it fits well in a smaller aquarium, but they would like to be in a group of at least five to six individuals, so the aquarium must not be too small either. They are excellent algae eaters but need support, and they are also quite sensitive. Therefore, it is best to introduce them when the aquarium has been running for a while, and the water values ​​are stable.

Amano shrimp

Amano shrimp (caridina multidentata) is one of the most popular algae eaters that’s not a fish. They are not actual herbivores but, in addition to algae, clean up most things in the aquarium, such as feed residues, dead plant parts, feces, etc. 

Their big advantage is that they do not reproduce as easily as some snails do because their fry requires brackish water to survive. They are best kept in a group of six or more individuals. They are peaceful but sensitive to nitrate.

Algae-inhibiting plants

By algae-inhibiting plants, it generally means aquarium plants that grow quickly, are good at utilizing the nutrients present in the aquarium water and can therefore compete with the algae. 

It is a reasoning that is not really correct but may work. Nitrogen and phosphorus are two essential nutrients for plants. Nitrogen occurs in the atmosphere in gaseous form. Plants cannot absorb nitrogen gas (however, cyanobacteria can, if the gas is dissolved in water) but absorb the nitrogen in its ionic form nitrate or ammonium.

Aquarium plants, with few exceptions, prefer ammonium as a nitrogen source and will assimilate it before nitrate. They can also store nitrate, which makes them a more stable source of nitrogen.

 Without going into too deep explanations, you can say that it is quite possible to have measurable nitrate levels in the water without noticeable algae growth—but as soon as you have measurable levels of ammonium and a light source, you will get algae in the aquarium. 

Therefore, it may be more relevant to review feeding and maintenance (more frequent water changes and removal of dead plant parts) than to reduce the supply of a qualitative plant nutrient that uses nitrate as a nitrogen source.


Ceratophyllum is a fast-growing, easy-care and common aquatic plant that can be planted in the bottom substrate or used as a floating plant. It is claimed that it also emits algae-inhibiting substances. It can withstand thinning regularly and is one of the plants that you can plant in the aquarium right at start-up.


Hygrophila is a plant whose natural habitat is in Asia. Like Ceratophyllum, it is one of the most suitable aquarium plants to plant in a newly started aquarium as it also grows very quickly. 

You usually have to limit its growth by pinching the outermost shoots, or otherwise, it can compete with other plants in the aquarium. The leaves are elongated and 1-1½  inches long—powerful aquarium lighting results in smaller leaves and shorter internodes.

Water plague (Egeria densa)

Water plague has a slightly greater need for light than Ceratophyllum and Hygrophila, but if you meet its still relatively small requirements, it grows both quickly and lushly. It is viable and manages under suboptimal conditions but can become thin and pale in color. It is easy to propagate through cuttings and is said to release substances that counteract cyanobacteria.


Vallisneria has an upright growth habit with long narrow foliage that does not shade other plants if you do not let it grow too high. This aquarium plant thrives best in an “airy” bottom substrate, and when it takes hold, it can almost quickly take over an aquarium. It multiplies spontaneously by sending out “tentacles”, i.e., elongated plant shoots from the root ball, which then take root and create new plants.


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