Do Algae Eat Nitrate? (As Well As Ammonia & Nitrite)

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

I always knew that aquarium plants can help against toxins like ammonia, nitrite, and nitrate. However, for quite some time, I couldn’t help but wonder whether algae would do the same thing.

Algae will consume nitrogen compounds, including ammonia, nitrate, and nitrite. The highest affinity is towards ammonia, which can be consumed pretty quickly. However, in the absence of ammonia, algae would eat nitrite and nitrates as well.

As we move forward, I will discuss how you can get rid of aquarium toxins using algae. Then, I will help you understand the nitrogen cycle and the role algae and aquarium plants play in it.

Hair algae that grow on plants are an excellent way to lower toxins like ammonia and nitrate.

Will Algae Eat Ammonia, Nitrite & Nitrate?

Algae is a plague in aquariums. It has its benefits. For instance, it can improve water chemistry by absorbing certain toxic substances. But that is only true in the short term. 

In the long-term, algae is a danger to fish, which is why many aquarists want to understand the relationship between algae and nitrates. 

That relationship can affect your ability to either nurture or eliminate algae. To understand how algae relate to nitrates, you have to keep the following in mind:

1. Ammonia

As you know, algae use all three nitrogen forms (Ammonia, Nitrites, and Nitrates) as fuel. But if algae had a favorite, it would be ammonia. 

A 2021 paper from the University of Naples Federico II (Giovanna Salbitani, Simona Carfagna) exploring sustainable wastewater treatment methods identified ammonium as the most convenient nitrogen source for microalgae, at least where cell metabolism was concerned.[1]

You can also look at a study from the Department of Biological Sciences (Boise State University, Boise), which identified ammonia as an effective fertilizer for algae.[2]

If you have a decent algae population, don’t be surprised if the nitrate levels are very low. The algae will consume ammonia before it can become nitrites and nitrates. In that regard, algae are technically beneficial.

2. Nitrites

What if the algae can’t find ammonia? Nitrates are the next best option. As the algae population grows, the nitrite levels will plummet. 

But this doesn’t happen overnight. If you went from having a significant nitrite content to zero nitrites within a short period, something else is at work. 

3. Nitrates

If the alga consumes the nitrites, nitrates won’t form. But if your tank lacks nitrites, any existing nitrates will fall prey to the algae.

Although, this process is not only inefficient but slow. If you introduce ammonia to your fish tank, the algae will abandon the nitrates.

Many people (and organizations) have noticed algae’s ability to eat nitrates. 

In fact, they rely on macroalgae (Gracilaria, Caulerpa, Sea lettuce, etc.) to reduce nitrate levels in tanks and water bodies.[3] Therefore, algae’s ability to eat nitrates is not the secret you may think it is.

If you’re tempted to experiment, you can use macroalgae types like Halimeda and Ulva to lower the nitrate concentration in your tank. These organisms can also lower phosphate levels.

Algae can be a nice touch to aquariums, especially when taking into account their biological advantages.

Pro tip: As opposed to ammonia, nitrate becomes toxic only when reaching relatively high concentrations of about 40 to 50 ppm. You can read all about it here.

More About Algae & Nitrogen Consumption

Of all the nutrients algae require nitrogen is probably the most vital. A paper in Ecology and Evolution exploring the influence of nitrogen on green alga identified ammonia as a critical component of algae growth.[4]

This is problematic because ammonia is commonplace in aquariums. Aquarists will cycle tanks before adding fish to nurture bacteria that convert ammonia into nitrites and nitrates.[5]

But this doesn’t help you because algae can feed on all three forms of nitrogen. You could argue that algae’s primary interest is nitrogen, and the form doesn’t necessarily matter. 

Algae can raise the pH by absorbing the nitrogenous compounds in your tank.

Will Diatoms Eat Nitrates?

Diatoms are not an exception. Brown algae are fascinating because they are not actually algae. Algae are comparable to plants. 

Brown algae consist of diatoms (single-celled organisms). You find diatoms in every aquatic environment, and even though they are not algae, they eat nitrates.

In other words, if you have brown algae in the tank, nitrate levels will fall in the same way they would if you had green algae.  

What Other Nutrients Do Algae Eat?

First of all, some people think that algae bloom when you expose a tank to excess light, but that is not necessarily true. Algae require a multitude of nutrients. 

For instance, like every plant in the aquarium, algae absorb carbon dioxide. If the carbon dioxide content is too low, it will use the water’s carbonate hardness.[6] If your pH is unstable, check the algae population in the tank. 

Algae will also consume phosphates, especially when they change from an insoluble form to a soluble state because of the decaying matter in the water. 

Potassium is another notable nutrient. Although, it is only problematic in planted tanks.[7] Simply put, many things must go wrong for algae to bloom uncontrollably. 

An abundance of light is not enough to choke your aquarium with this organism. It takes a combination of light and the right nutrients for algae to become a problem.

Pro tip: Algae are an excellent solution if you wish to get rid of nitrates. However, there are plenty of other useful solutions, as I explained in this article.

Planted tanks are less likely to suffer from toxins, including ammonia, nitrite, and nitrate.

How Does Nitrate Affect Algae Growth?

If you think that high nitrate levels encourage algae growth, you’re not the only one. Various studies have noticed that water bodies with significant algae growth have high nitrate levels.[8]

Experts from the University of Florida (Water Institute) took an interest in this topic because they had connected algal blooms in water bodies to nitrate pollution, which they blamed on water from waste disposal systems and agricultural fields.[9]

Although, their findings also noted that removing the nitrates wouldn’t necessarily eliminate the algae.

Some of their experts highlighted situations where the nitrate concentration was high, but algae growth was low. 

This isn’t surprising because every scientist recognizes that light and nitrates are just two ingredients among the various components algae require to thrive.

In the wild, algae populations will run amok because the oxygen content has fallen in some water bodies, killing snails that typically graze on algae. Oxygen levels drop because of flow reversals. 

The term ‘Flow Reversals’ refers to a situation where murky water from the river flows into a spring instead of clean spring water going to the river. 

You can’t connect the presence or absence of algae in every case to the nitrate concentration. Algae’s relationship with nitrates is complicated. 

It has many dimensions that you must understand to combat the threat effectively. Flow reversals cannot occur in aquariums. 

However, algae can still bloom for various reasons, including insufficient water agitation and poor maintenance.

A Little About The Nitrogen Cycle

Ammonia usually forms in fish tanks when organic matter decomposes. And yet, anything above 0 ppm can be toxic to fish.

Fortunately, in a healthy aquarium environment, bacteria called Nitrosomonas are responsible for turning ammonia into nitrite, which is far less harmful.

Then, bacteria named Nitrobacter consume nitrite and turn it into nitrate, which is the main nitrogen compound discussed in this article.

An illustration of the nitrogen cycle that is typically found in a healthy aquarium environment.

Then, aquarium plants, as well as algae, get rid of that nitrate. However, as I mentioned earlier, algae can easily consume ammonia and nitrite directly.

The essential bacteria standing behind the nitrogen cycle are mainly found in the filter media and form within six weeks in a brand-new tank (in a process called cycling).

That is why it is so important not to clean the filter media too thoroughly. Once a month, you can dissemble the filter to ensure it isn’t clogged with leftovers. 

However, when dealing with the filter media, merely rinse it with aquarium water.

You can help the nitrifying bacteria by vacuuming the aquarium substrate. That part usually contains a lot of debris and leftovers that produce ammonia.

For that purpose, I got the Laifoo Aquarium Siphon Vacuum Cleaner (link to Amazon). And frankly, I couldn’t be more satisfied. 

If you’ve never used an aquarium vacuum cleaner before, here is an excellent Youtube video that will walk you through it:

Pro tip: Dealing with ammonia is key when you find high nitrate levels in your tank. Here is an article with all the information you need about ammonia, including the specific products I use to remove it.

If you found this article helpful, these may also interest you:


Algae, as well as aquatic plants, play a central role in the nitrogen cycle. Without any intervention, they help get rid of toxins like ammonia, nitrite, and nitrate.

Of these three, the algae’s biggest affection is towards ammonia. That is pretty fortunate as this is the most dangerous toxin found in aquarium water.

By consuming ammonia, algae will prevent nitrite and nitrate from forming. However, even if some manage to form, algae make sure to remove them as well.

Nevertheless, you shouldn’t rely on plants and algae solely when fighting against toxins. Frequent water changes and routine maintenance are essential as well.