Algae is a nuisance that virtually every aquarium keeper will have to battle at some point. It is estimated that there is anywhere from 30,000 to over a million species of algae. Fortunately, the number of algae strains commonly seen in aquaria is fairly low, and few if any are actually harmful for the fish. Certain fish love to eat certain types of algae, so in some cases a small amount of algae can be beneficial. But for the most part we try to eliminate algae from our tanks because it looks bad, and why would anyone want to keep an ugly aquarium?

What is Algae?

There is some disagreement over what algae truly is, and there are some organisms that we refer to as algae that are very different from any true definition of algae.

Depending on the source, algae may be considered a plant or a protist. Blue-green algae, the slimy film algae that can quickly cover all surfaces of an aquarium, are actually a type of bacteria called Cyanobacteria.

Whatever the type, and however they’re classified, algae do share certain characteristics in common. Most notable of these is the ability to grow and thrive solely off the energy from light, even in the absence of many other nutrients. 

Algae Outbreaks

Even though algae are rarely harmful to a tank, you can easily draw parallels between algae in an aquarium and bacteria in a human body.

Every aquarium has a diverse range of algae present at virtually all times, much like people are hosts to a wide range of bacteria at any given time. However, as with people, if an aquarium is well maintained and taken care of, the natural processes of the aquarium will keep the algae in check and it will be unnoticeable. There are even certain types of algae that play beneficial roles in aquaria just as there are beneficial bacteria that play invaluable roles in your body.

However, when this balance is interrupted, an outbreak can easily occur. The systems get thrown off and the algae that was being kept in check begins to flourish, taking over and wreaking havoc. Fortunately, once you know what conditions are ideal for algae, you have a pretty good idea of how to avoid letting it get out of hand.

Do you want algae? Because that’s how you get algae.

Much like plants, there are three factors that determine how well algae will thrive. Just like plants (remember, algae may or may not be considered plants, depending on who you ask), algae need light, nutrients, and air (generally carbon dioxide). However, the ratio of these factors that different algae need are different from the plants we want to keep in our tank, and there is going to be some type of algae that will happily take advantage of almost any set of conditions.

How are algae able to get these needs met? They are provided (either intentionally or inadvertently) by the aquarium keeper.

Light may come from the light you put on top of your aquarium to illuminate it for yourself (or the plants you are trying to keep), or it may come from ambient sources (such as sunlight through a window). It can be hard to know exactly how much light your aquarium is receiving without the use of expensive equipment, but it’s fairly easy to remember what sources tend to be brighter or weaker than others.

By far the most intense light is direct sunlight, even if filtered through a window. For most people, it will be impossible to control algae if the tank is kept in direct sunlight. There are a number of different aquarium lights available the supply different amounts of light. Lights designed for keeping photosynthetic organisms (such as keeping planted aquaria or live corals) are going to be brighter than lights designed simply for viewing. Ambient, indirect room lights can range from fairly intense (if there are a lot of windows allowing a lot of sunlight to bounce around) to fairly inconsequential (for example in a basement with no windows).

The nutrients used by algae, like the nutrients used by plants, mostly come from nitrogenous sources. Ammonia, nitrite, and nitrate are the primary nutrients, and algae will usually take their fill faster than your beneficial bacteria can break them down.

As you should know from learning about the Nitrogen Cycle, these nutrients can come from a wide range of sources. Overfeeding your fish and overstocking your aquarium are probably the two most significant sources of nitrogen in your aquarium. Uneaten fish food, dead fish, or rotting plants are also common sources for nitrogen. All of these need to be considered and kept under control.

Finally, air is a factor that most keepers will have limited impact on and that may or may not affect algae growth in a tank.

The major exception here happens when someone is keeping a heavily planted aquarium in which they are providing a lot of extra light and nutrients to encourage plant growth. In this case, if the aquarist does not provide enough supplemental CO2, the plants will begin to use it up. This limits how much of the nutrients and light they can use, and those extra nutrients and light will then fuel algae growth.

Avoiding Algae Growth

If light, nutrients, and air are the factors that fuel algae growth, then those are the factors you need to address in order to avoid algae growth.

The Basics - Balancing The Factors

In most cases where algae is a problem, it’s the result of having too much light and/or too many nutrients in the water. Thus, for most cases, take steps to reduce these.

If your tank is near a window, move it to a darker part of your house. Choose a light fixture that doesn’t give off as much light or reduce the amount of time your lights are turned on. There are some LED fixtures that look incredibly bright, yet don’t actually put off much light energy, making them great to view your tank without fueling algae.

Don’t feed your fish as heavily, or remove some fish from your tank to reduce the amount of nutrients they’re putting into the water (maybe a good excuse to buy a new aquarium?). Increase the frequency of your water changes in order to physically remove nutrients.

That may seem to be an oversimplification, but most of the time it really is that easy to solve an algae problem. That doesn’t mean that this solution isn’t going to take some effort and patience, just that you have a straight forward approach to solving the problem.

Planted Aquariums

If the factors that fuel algae growth are largely the same as the factors that fuel plant growth, then you may think that adding plants could help reduce the algae in your tank. If handled correctly, you would be right!

With a planted aquarium, it’s easy to set up your tank in such a way that the plants will use up nutrients fast enough that algae can’t compete. However, you do need to do some research and planning or else you may end up in a situation where you give algae the advantage.

Keeping the three factors balanced is key. If you get strong lights but don’t fertilize your plants, you’re going to get algae. If you over fertilize without giving enough light, you’re going to get algae. If you give too much light and nutrients but don’t supplement CO2, you’re going to get algae.

Most planted aquarium keepers who take the time to learn how to give optimal care to their plants eventually discover that they stop having algae problems altogether. But you do need to put the effort in to learn before you can see those results.

An Underrated Approach

There is one method that is extraordinarily underrated and neglected: create a riparium.

What’s a riparium? Essentially, it’s a setup where non-aquatic plants are planted in containers at the top of an aquarium with only their roots in the water. Certain terrestrial plants who can tolerate or thrive in extremely moist conditions can be used, as can some aquatic plants that can grow emersed (i.e. with their leaves out of the water). Marginal plants, which naturally grow on the edges of bodies of water, are perfect for this setup.

Why are ripariums such a good choice? Because you don’t have to worry about penetrating through water you don’t need as bright of light and can elevate your fixture significantly further from the top of the tank, which reduces the amount of light available to the algae. Additionally, the riparian plants will often shade much of this light from reaching into the tank. You don’t have to worry about CO2, because they receive a constant supply from the atmosphere. Finally, because they often grow much larger than aquatic plants, your riparian plants will suck a huge amount of nutrients from the water. The result is a tank with a low amount of light and virtually no excess nutrients, which doesn’t give algae a chance to get a foothold.

There are a few challenges with ripariums. Perhaps most significant is that, due to them being relatively unpopular, there’s little if any equipment commercially available to set up a riparium, so it will take some creativity to put one together. You also have to consider the size of the plants you use and ensure you have enough space for them to spread and grow.

Fighting Algae With Algae Eaters

It’s always better to eliminate the source of algae rather than try to control it after the fact. But if you but if you’re looking for some ways to reduce algae that’s in your tank, there are a lot of animals that will happily eat algae. Spend some time considering what will best satisfy the needs of your tank.


Arguably one of the best animals for eating snails in many tanks are snails. There are certainly snails that have a well-deserved reputation for multiplying endlessly and becoming a major nuisance, but there are also species that are much more manageable.

A great option for tanks are freshwater nerite snails. These snails are ravenous for algae, and can be very efficient at removing many common types of algae. Additionally, they stay small and can be kept with aquarium plants without destroying your aquascaping. Best of all, while they live in freshwater, their eggs can only hatch in saltwater, meaning that you don’t have to worry about unwanted population growth.

Other snail varieties also make good additions. Rabbit snails are effective and have a unique appearance that stands out from other snails. Many people are fans of apple snails as well, though keep in mind with these that they do have the potential to grow quite large, to sizes around 4-5 inches in diameter.


Among planted tank enthusiasts, particularly those who keep small tanks, certain shrimp are renowned for taking care of spare algae without harming their plants. Best known for this are the Amano Shrimp, but most shrimp varieties will likely eat at least a little bit of algae. Plus, shrimp have a certain amount of charm it’s almost impossible not to fall in love with.


Plecos are the first fish that many people think of when they hear the words algae eater. However, there are many plecos that are not good choices for various reason.

The common pleco is one such fish. While there are a lot of good things about common plecos, they have some challenges that make them a bad choice for many aquarium owners. The first is their sheer size, which can get up to two feet in length. Additionally, their diet is more centered around various organisms that live on driftwood. Algae will be consumed, but it’s not really the main diet for them. Because of their large size and the amount of wood they eat, they tend to be very messy fish.

One of the best plecos to get for algae control is the bristlenose pleco. They stay small enough (around 6 inches) to be manageable in most aquariums and algae is a much larger proportion of their diet than it is for common plecos. They also tend to not mess up aquarium plants, making them good choices for planted tanks.


If you have a tank with small, peaceful fish, otocinclus are potentially one of the best algae eaters you can choose, though they’re not without challenges themselves. They stay very small, barely getting over an inch in length, which makes them incompatible with many more aggressive fish. They also have the reputation of being somewhat sensitive and fragile, so you want to ensure you have a well established aquarium with stable water parameters. But if you can provide a suitable aquarium, a school of otos is a great choice.

Flying Fox

True flying foxes are another great choice, though there are some extremely similar (and less effective) species that can create difficulty in finding the correct fish. However, once you find some flying foxes, they do a great job of eating many different types of algae, including black beard algae that many other algae eaters won’t touch. They are quite peaceful and hardy, typically growing to around 5 inches.

As a note, one fish that is widely available and sometimes gets confused with flying foxes (even though they are fairly different and easy to distinguish) are Chinese algae eaters. While these do a decent job when they’re young, as they grow they become increasingly carnivorous and aggressive, making them a bad choice for most cases.

Just the Beginning…

It would take many more pages to fully talk about all the nuances of algae in aquariums. It can be valuable to know what different types of algae we typically see, what factors feed into which type of algae, and the best way to combat them. This is a very short look at the animals that eat algae, and there are many others that could be discussed.

But it should give a starting point for learning how to control and minimize how much a nuisance algae will be for you.

What are your experiences with algae? Have you had any legendary battles with it, or discovered some novel way to prevent it? Is there an algae eater that you particularly prefer? Let us know in the comments!