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How to Lower Nitrate Levels in Freshwater Tank Aquarium in 4 Simple Steps

The nitrogen cycle ends with nitrate as the final product in your aquarium. Very often, you may have heard that nitrate is harmless to your freshwater aquarium and that is correct but is highly susceptible to misinterpretation. In other words, nitrate poses a potential challenge in certain quantities. Aquarists tend to go all out to combat ammonia and nitrite but become lax when it comes to nitrite; this is a big risk.

This article aims to expatiate on how to lower the level of nitrate in freshwater aquaria. Before sharing this, it is imperative to define the terms that constitute the subject matter, the causes of high nitrate levels in freshwater aquaria; as well as the consequences of a nitrate level surge in your aquarium.

Freshwater fish vary in anatomy and physiology from saltwater fish. Typically, freshwater fish are built to retain body fluids because there are not many of those in their natural habitat. They also have large kidneys that are well-developed to process a lot of water. That being said, freshwater fish are very adaptive and that is why beginner aquarists prefer to have freshwater fish in their aquarium, not a bad choice at all!

This article’s spotlight is on how to lower a high nitrate level in your freshwater aquarium if you’re experiencing that. If you are not, this article will inform you of how to keep nitrate levels in control, so follow along!

Causes of Surge in Nitrate Level

Nitrate is the broken down version of nitrites by beneficial bacteria in your aquarium and is not to be dismissed as non-toxic; it causes problems to your fish if not properly managed such as:

Stunted Growth: High levels of nitrate can affect the growth of young fish especially. If you have not been checking and monitoring the nitrate levels in your aquarium, you may want to get to it now to avoid slowing down the biological development of your fish.

Stress: The presence of concentrated nitrate in your freshwater aquarium will affect the psychology of your fish. This is as a result of the destabilized oxygen levels in your tank commonly caused by nitrates. With inadequate or unstable flows of oxygen, your fish stand the risk of falling sick or worse. Your aquarium and its inhabitants are meant to bubble with life, not be torpid.

Algae bloom: Algae feed on nitrates; and if your aquarium is full of them, you are inviting algae to your freshwater tank. Algae infestation is one of the biggest problems potentially facing any freshwater aquarium; not only do they give an unsightly outlook to your tank, but algae also pollute and eventually kill aquatic plants and animals.

Blotch Break-outs: If no precautions are taken, fish exposed to nitrate at high levels, for some time, may begin to fester sores on their skin and become very lethargic; this condition is known as nitrate poisoning.

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The effects of accumulated nitrates can be as dangerous as the smallest quantity of ammonia and nitrites. This begs the question of what causes nitrates to accumulate in freshwater aquariums.

Causes of Nitrate Accumulation

Certain habits contribute to the rise of nitrate levels in your freshwater aquarium and unlike its predecessors in the nitrogen cycle; nitrate is harder to physically detect. It is odorless and does not affect watercolor or physical features. Hence, it is important not to always assume that all is well in your aquarium. A surge in nitrate levels is usually as a result of one or all of the following:

Overcrowding your freshwater aquarium

When your fresh water tank is overfilled with fish, it becomes increasingly difficult to keep up. Too many fish in release too much waste than your aquarium can handle and the end product of the nitrogen cycle is a staggering level of nitrate.

To avoid this problem, ensure that you only have a minimal number of fish in your aquarium at a time; and according to the size of your tank. If you must add more fish, we highly recommend that you purchase a bigger tank. Consequently, your fish have enough space to move around and you can monitor their activities easily.

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Overfeeding your fish

This is linked to the first point, but even a few fish can be overfed. Perhaps in a bid to give your fish the best care, you go over the top with food rationing. Your intentions are noble but you are doing more damage than good to your fish and your aquarium as a whole.

Excess food left uneaten will significantly add to the quantity of waste in your water. Apart from risking an increase in nitrate levels, your aquarium becomes prone to an algae bloom.

Decaying Plants

It is correct that aquatic plants absorb nitrate as an essential nutrient, however, if these plants dry out and fall out of their roots; they begin to decompose and if not immediately evacuated, they add even more waste to your water. This build-up of toxic waste results in high nitrate levels.

Inadequate maintenance routine

This is another common cause of nitrate booms, caused by undermining the potential danger of nitrate. This coupled with laxness in carrying out maintenance tasks such as cleaning your filter and changing water. A dirty water filter and stale water will shoot up the nitrate level in your aquarium.

Nitrate Level

As a beginner aquarist; or one that is just getting to know about the dangers of high nitrate levels in the water, you must be curious as to how much nitrate is manageable and at which point you should get concerned.

Some websites will inform you that nitrate levels below 100ppm are relatively safe and nothing to worry about, but we beg to differ. It is better to prevent than to cure and that is why we recommend that you treat your water once the nitrate levels rise to 30ppm to 50ppm.

Ideally, nitrate levels should be kept below 10ppm; therefore, you may pay it no mind if it is on 15ppm or 20ppm; anything above that calls for immediate attention to prevent the situation from spiraling out of control.

Keep close observation of the water chemistry in your freshwater aquarium using original home testing kits, and take safety precautions on time to avoid the surge.

How to Lower Nitrate Level in Freshwater Aquarium


If your aquarium is freshwater, the most effective means to lower the nitrate level in your water is by changing your water; partial water change. The process of water changing is one of the most important maintenance routines in the aquascaping hobby.

Water left unchanged become stale as a result of the chemical and biological activities going on in it. It is also the easiest way to get rid of that entire nitrate. The logic is pretty simple; you get rid of the water, you get rid of the nitrate therein.

But before you get to it, take note of the word ‘partial’; that means you do not get to pour out all the water in your tank and refill it with new water. Why?

We earlier discussed freshwater fish and how quickly they adapt to their environment. Fish; freshwater and saltwater fish alike, are very sensitive to change. This means that they are immediately aware of the slightest changes in their habitat such as water chemistry and temperature, and they react to it extremely.

Suddenly changing the water they live in can kill them. There is toxic nitrate in the water, but in a bid to save them and your freshwater aquarium, you have to follow a procedure so you do not wind up causing more harm to the fish.

When changing your water whether as a maintenance routine or to rid your freshwater aquarium of nitrate, you are only expected to change a part of your water; typically not more than have.

A partial water change to remove nitrates is also done in phases: lightly vacuum your substrate and remove only about 15% of the water per day and refill with new freshwater. Continue this until you have removed about half the water; this dilutes your freshwater and reduces the nitrate level drastically, without shocking your fish. - For all your creative needs!


Adding plants to your freshwater aquarium is a biological method that will prove quite effective in the reduction of the nitrate level in your water. Nitrate is one of the nutrients needed by aquatic plants to grow, so if you need your aquarium’s nitrate level in check, aquatic plants such as anubias, java ferns, java moss Amazon swords, and mangroves will make a great visual addition to your freshwater aquarium and relatively lower nitrate level. It is, however, important to note that plants can only take in the number of nutrients that they need per time. In the case of excessive nitrates available, this step may not be as effective as outright water changes.


These nitrate-absorbing filter media and anaerobic denitrifying biofilters come in the form of pads and sponges used to remove nitrate from your freshwater aquarium. While these may prove handy, they do not remove the root cause or permanently solve the problem.

Using filter media is however an excellent means of preventive measure against the rise of nitrate levels and keeping it below the danger bar. Nitrate-removing resins and chemicals also fall under this category.

The aforementioned steps; notably water change tops the list as a very reliable, easy, and potent means of curbing the rise of nitrates levels in freshwater aquarium. To keep up with the activities of the nitrates:

  • Purchase original home testing kits from a credible supplier to monitor water PH, ammonia, nitrite, and nitrate levels in your freshwater aquarium.
  • Keep a daily record of measured levels of nitrate and observe the rise. If it needs preventive measures, be proactive, and take them.
  • Study the nitrogen cycle and its effects on your freshwater aquarium.
  • Before adding aquatic plants to your freshwater aquarium, ensure that they compatible with your fish and they serve the purpose of regulating nitrate levels


Nitrates are a natural part of your freshwater aquarium, and as long as you keep it check by following the steps given in this article, you are prolonging the life span of your fish, plants, and aquarium environment. It is worthy of emphasis that either as a fish keeper or aquarist or aquascape hobbyist, research is needed for every method you employ and every step you take.

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Freshwater aquariums are slightly different from those of saltwater; study those to get a solid knowledge of how to handle your aquarium. A healthy aquarium not only creates a happy environment for your fish and plants, but it also makes the aquarist happy and fulfilled.