How to Reduce Nitrate levels In an Aquarium?

How to Reduce Nitrate levels In an Aquarium? This is the big question here.

Did you know that Nitrate (a by-product of the Nitrogen cycle) is a potential toxin for your fish?

The most common mistake committed by fishkeepers is their negligence towards the toxic substances present in their aquariums. Such harmful agents include high levels of ammonia, nitrites, nitrates, and CO2, etc.

If neglected for prolonged durations, such substances can end up killing your fish. Increased nitrate level is one of the most common causes of fish diseases and eventually mortalities. Nitrate toxicity can affect your fish’s digestive and respiratory system and can even prove fatal.

This article will highlight the harmful effects of nitrate toxicity, its causes, treatment, prevention, and much more. So, stay tuned and get the answers to most of your nitrate-related queries.

What is Nitrate, and what are its sources?

Nitrates are compounds consisting of one nitrogen and three oxygen atoms (NO3). They are relatively inert, which means they are stable and unlikely to change and cause harm.

Sources of Nitrate:

Nitrate is an end-product nitrogen cycle (which will be discussed later in this article). Nitrates are around us everywhere in human bodies, food, vegetables, and especially in meat.

Moreover, freshwater and rainwater also contain high levels of nitrates. Thus, it is crucial to carefully monitor the nitrate levels in the water source you are using for the Aquarium.

Nitrate Concentration in Tap Water:

To our surprise, the tap water is loaded with nitrates. It has been recently found that tap water in different areas around the globe has more than 35-40 ppm of nitrates. This is shocking and worth pondering as well. Thus, this water is like a death sentence for your aquarium fish.

In addition to the water added, there are more sources of nitrate production in the Aquarium. Majorly Nitrates are contributed by decaying fish waste, leftover food particles, decomposing plant material, and debris.

Thus, it is vital to maintain a system of combating and disposing of this hazardous agent; otherwise, you are at risk of losing your dear fish.

What is the nitrogen cycle?

Generally, the nitrogen cycle is a biogeochemical cycle working to eliminate high nitrogen levels by converting them into nitrates, nitrites, and many other by-products.

The nitrogen cycle is an essential component of the aquatic ecosystem and thus of the Aquarium as well. There is a continuous buildup of ammonia in a fish aquarium due to fish waste, plant debris, and decaying food particles.

To eradicate rising ammonia levels, nitrifying bacteria such as “Nitrobacter” and “Nitrosomonas” convert ammonia to nitrates and nitrites.

Thus, the nitrogen cycle is an inevitable nitrate source and a necessary evil for the aquatic ecosystem.

Safe levels of Nitrate in the Aquarium:

Nitrate levels in different environments can vary according to the species inhabiting that area and prevailing conditions. In this respect, the levels of nitrates differ in both freshwater and saltwater habitat. So, a fishkeeper must know the desired levels of nitrates according to the fish and its habitat.

Ideal Freshwater Nitrate Levels:

The ideal levels of nitrates for a fish inhabiting freshwater zones are around 20-25 ppm but precisely 25 ppm. Levels above 45-50 ppm are strictly prohibited by fish experts as such high levels are detrimental to the health of your fish.

It is advised to follow extra precautionary measures when it comes to breeding freshwater fish tanks. In this case, levels should not exceed more than 10 ppm. The lower, the better.

Ideal Saltwater Nitrate Levels:

Maintaining adequate levels of nitrates is even more crucial in the case of a saltwater aquarium. The maximum bearable limit for a saltwater aquarium is 5 ppm.

Such low levels are advised as invertebrates, corals, and saltwater fishes are particularly sensitive to rising nitrate levels. Frequent water changes must be performed to keep nitrate levels in control while keeping an eye on the salt content of the Aquarium.

How to Determine Nitrates level in the Aquarium?

Thanks to the advancing technologies and extensive studies on aquatic life, we have several methods to check water parameters. In the case of nitrate level testing, three primary methods are helpful in accurately determining these levels.

Paper Strip Test:

This method is relatively easy, effective, and cost-friendly. In this process, the test kit contains a paper strip and a color chart. The color chart has different colors denoting different levels of Nitrate detected.

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The main thing to do is take a test sample from the Aquarium and dip the paper strip in water. Within a minute or so, the strip will magically change its color. Now compare the color of the strip with the color chart provided.

The matched color is your answer to nitrate concentration. Although this method does not provide an accurate value, it is pretty helpful in indicating the situation.

Liquid Reagent Test:

The second most widely used test for determining the nitrates level of the Aquarium is a liquid reagent test. As the name indicates in this method, the test kit contains a testing reagent.

All you need to do is take a small concentration of aquarium water in a test tube with the help of a pipette. Now add in the test reagent ad wait for the magic. After some time, the solution will change color; the acquired color should match the color chart. The suitable matched color indicates the concentration of Nitrate in the Aquarium.

The pipette, test tube, reagent, and color chart are parts of the kit, 0so you don’t have to worry about that. This method is quite efficient, time-friendly, and inexpensive as well.

Master Test Kits:

Nowadays, master testing kits are available in the markets without a doubt a solution to many aquarium problems.

Through these master kits, you can determine the pH, water hardness, nitrate, nitrite, and ammonia levels simultaneously. These kits are cost-effective as it is beneficial to purchase one kit that can master all rather than buying a separate kit for each water parameter.

Types of Nitrate Toxicity:

High levels of nitrates in an aquarium can be quite detrimental for your fish. In addition, the time of toxicity is also a crucial factor to count.

Thus, nitrate toxicity prevails in two distinct forms.

Nitrate shock:

Nitrate shock is an acute form of toxicity. In this condition, fish is exposed to sudden high Nitrate levels, reaching up to 100 ppm. Any drastic change in nitrate levels, whether increasing or decreasing, leads to a severe form of nitrate shock.

Fish is surprised by such a high concentration of Nitrate and is unable to fight such conditions. In nitrate shock, fish usually dies within or less than 24 hours. The significant causes of nitrate shock or acute nitrate toxicity are the following.

  • Unnecessary water changes leading to a sudden spike in nitrate levels. It is more common in newly developed tanks where it is challenging to combat high nitrate levels, and fish goes into nitrate shock.
  • Suppose a new fish is introduced in a poorly kept tank having high nitrate levels. Fish is new to this environment and is not capable of combating such toxicity.

Nitrate Poisoning:

Nitrate poisoning is a more gradual and continuous form of nitrate toxicity. It occurs when a fish is exposed to increasing concentrations of Nitrate over a long period. Thus, calling it “chronic nitrate toxicity” will not be wrong.

 Although, this process takes up to weeks or months, and your fish will be acclimatized to such dangerously high levels. But once the conditions are out of hand for too long, your fish may die.

Causes of Nitrate Poisoning:

Small and delicate fish, primarily saltwater fish, cannot withstand such conditions for too long and will die soon. The main reasons behind nitrate poisoning are the following.

  • Overcrowding of Aquarium means more waste products and more nitrates in the Aquarium.
  • Overfeeding will lead to increased levels of fish waste and decaying fish food. Ultimately contributing to nitrate toxicity.
  • Poor tank maintenance, with inadequate water changes, results in excessive buildup of nitrates in the Aquarium.
  • If poor quality water is used, that is loaded with nitrates such as tap water. This will lead to dramatic nitrate poisoning in no time.
  • If water parameters are not tested regularly, such negligence can cause nitrate toxicity for a long time, with you being unaware of it.

Factors leading to Nitrate Accumulation:

You can only prevent the nitrate levels from rising if you correctly know what is causing a sharp rise in them. Thus, it’s an essential job of a fishkeeper to check the following matters to ensure accurate nitrate levels.

  • Overfeeding:

Overfeeding affects nitrate concentration in two crucial ways.

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1-First it will lead to increased waste production and thus loading the Aquarium with ammonia and ultimately nitrates.

2-Secondly, fish will be unable to consume such an abundant food supply, which will lead to surplus food in the tank, which will eventually decay and contribute to increased nitrate concentration.

Moreover, it can also affect fish’s digestive system and result in bloating, constipation, or swim bladder disease.

Thus, it is essential to understand the diet and requirements of your fish and feed them accordingly. Make sure to feed in a small amount 2 or 3 times a day, and you can skip some meals as well to boost up their metabolism.

  • Overcrowding:

Every fish has its requirement for space; thus, it crucial to provide them the room to grow. Overstocking the Aquarium can contribute to increased wastes in the tank, eventually becoming toxic for your fish. An overcrowded tank is no more than a nuisance for your fishes and can put them under immense stress.

So, while stocking your tank, keep in mind the aquarium size and provide appropriate space for your wish to grow properly. Young ones and territorial species need more space than others. Keep all this in mind while stocking your Aquarium.

  • Poor tank maintenance

It has been frequently experienced that in a well-kept tank, the incidents of nitrate toxicity are pretty low. Thus, regular water changes, substrate, and filter cleaning, and using biofilters, are inevitable. In addition, keeping appropriate water parameters in the tank can make a huge difference.

Sometimes, the filtration system is densely clogged with debris and waste products instead of cleaning the Aquarium, making it even dirtier. So, cleaning the filters is an important measure to avoid nitrate buildup.

  • Poor water quality:

As has been mentioned before, the water quality can significantly contribute to nitrate overload. The tap water ad other water sources are concentrated with nitrates. So, replacing this water with fresh or filtered water will make a significant difference.

Another method to improve water quality is to use reverse osmosis units to eliminate toxic agents from water essentially.

Effects of Nitrate Toxicity on Fish:

Exposure to rapidly increasing nitrate concentration can affect your fish’s vital organs. The very first systems that are affected are the respiratory and digestive systems. Soon enough, the integumentary system will also show signs of stress. In addition, the pattern and speed of movement will become abnormal as well.

The most common symptoms noticed in acute or chronic nitrate toxicity are the following.

  1. A slow and disoriented pattern of movement.
  2. Curling up of the whole skin.
  3. Rapid flapping movement of fins.
  4. Loss of appetite or unable to eat.
  5. An elevated rate of respiration accompanied by increased gill movement.
  6. Laying down on substrate and inability to move or swim.

If you notice any of the symptoms mentioned above in your fish, it’s your indicator to check water parameters, especially the nitrate levels.

Effects of Nitrate Toxicity on Plants:

These toxic substances affect the fish and are also responsible for the death of plants due to algae blooming. Nitrates contribute to the production of harmful algae in the aquarium water. This alga can grow tremendously supported by continuously increasing concentrations of nitrates.

Excessive Algae Production:

Overgrowth of algae can lead to depletion of oxygen in the tank that will ultimately cause the plants to wilt and die. Thus, the damaging effects of nitrate toxicity are not limited to fish only, but it can even destroy the whole aquatic ecosystem.

Treatment of Nitrate Toxicity:

If your fish is going through nitrate poisoning or nitrate shock, you can help your fish in its struggle to survive.

Avoid Feeding For a Day:

The first step you should take is to stop the food supply for a day or two completely. This step will help improve nitrate levels by decreasing waste production. Thus, eliminating any chance of increasing nitrate concentration.

Next, any radical change, whether increased or decreased, will put your fish in more shock and stress. Water change is your only solution to this problem but be cautious in performing water changes. If you quickly reduce the nitrates by changing 50% of water, your fish will die of this sudden stress.

Then what should you do?

Water Replacement in Steps:

The answer is removing no more than 5-10% each day, starting with light vacuum cleaning and remove waste from the upper part of the tank. Make your way toward the substrate with regularly changing aquarium water with fresh water. Eventually, this way, you will replace 50% of water in a week without putting any unnecessary stress on your fish.

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Remember if you remove 5-10% water every day and make it effective by replacing it with clean nitrate-free water. If you replace this with tap water, you aggravate the situation by adding more nitrates until it becomes a vicious cycle.

Remember the Target:

Keep in mind the target concentration of nitrates that you are trying to achieve is around 20 ppm. Thus, it is vital to check the nitrate levels with each water change. Once you reach your desired range, stop changing water.

Maintain the Accurate Levels:

The next and most critical step is to maintain these levels. Your job is not finished with just reducing the nitrates. The more significant part of your job is to keep the suitable levels all the time.

Tips to Reduce Nitrate Levels in the Aquarium:

Keeping nitrates within a limited range may sound complicated, but it is pretty doable. All you need to do is to follow these simple tips, and you are good to go.

  1. Perform partial water changes twice a month.

  2. A light round of vacuum cleaning once a week.

  3. Check the water parameters, including pH, temperature, water hardness, levels of ammonia, nitrates, and nitrates on a regular basis.

  4. Use high-quality water or install reverse osmosis units to reduce the nitrate content of water essentially.

  5. Nowadays, particular Nitrate eliminating filters are also available in the market; these filters can reduce the nitrate content of the tank significantly.

  6. Using microbes specialized for consuming nitrates as food sources can essentially lower the nitrate levels in aquariums. The correct use of these microbes requires experience, so use these microbes with complete guidance at hands. A perfectly established microbes’ community will lower the nitrate toxicity effectively.

  7. Moreover, established macroalgae communities can also eliminate the unwanted nitrates and phosphates from the Aquarium. These macroalgae colonies can be instituted in a refugium.

  8. Live plants are a natural source of nitrate consumption for their growth. Consequently, they are an epic and durable strategy to eliminate toxic nitrate accumulation naturally.

Precautions to Avoid Nitrate Buildup:

If you tend to sustain stable nitrate levels in your tank for the long term, you should avoid the following things.

  • Avoid using tap or regular water for the Aquarium.
  • You should refrain from overstocking your Aquarium.
  • Do not overfeed your fish.
  • Avoid cleaning all the substrate at a time; this will eliminate essential Bacterias from the Aquarium.
  • Do not leave dirty or clogged filters in the Aquarium.

Frequently Asked Questions (FAQs)

Some of the most frequently asked questions by most of the fish keepers are following.

1-What happens if nitrate levels are too high in a fish tank?

An increase in nitrate levels up to 100 ppm can cause nitrate toxicity. Such elevated levels can affect the digestive, respiratory, and immune of your fish in the worst way possible.
Moreover, there will be excessive algae production that can destroy the Aquarium’s ecosystem in no time.

2-What are the signs of nitrate poisoning in fish?

Acute or chronic nitrate toxicity can manifest itself through the following signs and symptoms.
1Rapidity and difficulty in breathing.
2Restlessness and irritability.
3-Loss of appetite and rejection of food.
4-Curling up of fish skin.
5-Rapid gill flapping.
6-Disoriented swimming

3-Will high Nitrate kill fish?

Although Nitrate is not that poisonous or detrimental for your fish, a sudden sharp rise in nitrate concentration can put your fish in nitrate shock. Such a shock or chronic, long-lasting toxicity can weaken a fish’s immune system badly.
Such immunologically weakened fish can die if left untreated. Thus, high nitrate levels can for sure kill your fish if neglected.


Nitrate toxicity is a real thing and can be very troublesome for fishkeepers and fish as well. But the good thing is that it is easy to treat and prevent; only a little effort can save your fish from so much damage.

We hope that this article will help avert this situation and prevent it in the longer run. BEST OF LUCK WITH YOUR AQUARIUM!!

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