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How To Add or Remove Nitrates in an Aquarium

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by Jason Matthews



Nitrates are a critical part of the internal ecosystem of your aquarium. Like the PH, TDS, and temperature, you should monitor your tank’s nitrate levels constantly to maintain the health of your aquarium and the plant and animal life inside it.

The best way to increase nitrates in an aquarium is to allow the nitrate cycle to stabilize and regulate itself. Regularly dosing with potassium nitrate is also possible, but you must do this carefully to avoid overdosing and poisoning the fish. 

Often, problems that people think are caused by nitrates are in fact caused by an imbalance in other minerals, like phosphates. Read on to learn about the causes of nitrate imbalances and what you can do about them. 

What Are Nitrates?

Nitrates are nitrogen-based compounds that are present in fish waste and urine. Nitrates are the least toxic part of the nitrogen cycle. Ammonia (which is present in fish waste and urea) breaks down into nitrites, which then break down into nitrates.

Nitrates are not inherently bad for your fish tank—they provide a necessary food source for the plants in your aquarium! 

Causes of Low Nitrates

It’s best to maintain low levels of nitrates in your aquarium for the health of your fish. However, sometimes, nitrate levels can become too low. 

This can sometimes happen if your tank contains a lot of plant life. Plants absorb nitrates through their roots and leaves. They use nitrates as a supply of nitrogen, which helps them build the proteins that they need for healthy growth. 

When there are lots of plants in a tank and not many fish to produce waste, the plants can use up all the nitrates, meaning nitrate levels can drop to zero.

Why Is Maintaining the Nitrate Level Important?

aquarium with healthy nitrate levels

An aquarium is a closed ecosystem. Everything that changes inside the tank affects everything else in the tank. Large fluctuations in PH, temperature, or levels of molecules like nitrates can throw off the balance of the ecosystem and lead to problems. 

When the nitrate levels in your tank drop to zero and do not recover, the plants in your tank may start to die. While live aquatic plants are not a necessity for a functioning, healthy fish tank, they do provide some major benefits:

  • They make oxygen
  • They filter carbon dioxide, ammonia, and nitrates
  • They reduce algae growth
  • They provide shelter for fish

If your plants die it will put more strain on your filtration system and can affect the quality of your water. It can also lead to an algae bloom.

How To Add Nitrates to an Aquarium

In general, if you are a novice fish-keeper and your tank is not yet well-established, it’s best to let the nitrogen cycle stabilize itself. It can take a few weeks for the cycle to establish as the fish produce waste and the plants use it.

Take regular readings of not only the nitrates in the tank but also the nitrites and ammonia levels. If there is no buildup of nitrites or ammonia, you don’t need to worry. 

Dosing With Potassium Nitrate

If you have an established tank with very low levels of nitrogen, you can try regularly dosing the tank with potassium nitrate. This is the safest way to add nitrates to an aquarium. Potassium nitrate is a fertilizer that provides both potassium and nitrogen to plants.

Potassium aids in photosynthesis and the production of chlorophyll. Photosynthesis is the process by which plants turn light and carbon dioxide into food. Chlorophyll is what gives plants their green color.

The amount of potassium nitrate you need will depend on the size of your tank and the number of plants and animals in it. Be careful to read the label and instructions on whatever product you buy, as overdosing the tank can lead to nitrate poisoning.

Last update on 2023-09-21 / Affiliate links / Images from Amazon Product Advertising API

Nitrate Poisoning

Far more dangerous than low levels of nitrates in an aquarium are high levels of nitrates in an aquarium. In a freshwater aquarium, nitrate levels should be below 20ppm (parts per million). Anything above 50ppm can cause nitrate shock or nitrate poisoning.

Symptoms of Nitrate Poisoning

sick fish from nitrate poisoning

Symptoms of nitrate poisoning present themselves over some time. They usually occur in fish who have received prolonged exposure to elevated nitrate levels. Symptoms include:

  • Abnormal swimming
  • Lethargy
  • Breathing problems
  • Fading color
  • Curled body

Some fish will not start to feel the effects of nitrate poisoning until the level hits 100ppm or higher. However, this doesn’t mean that you should ever let the nitrate levels in your tank get that high.

Related article: How to increase CO2 in your aquarium

How To Treat Nitrate Poisoning

Once nitrate levels become too high in a tank, it can be difficult to lower them. Clean your tank regularly and always check nitrate levels after each cleaning to prevent an imbalance in nitrate levels. Act quickly if you notice any of the symptoms of nitrate poisoning in your fish. 

Change the Water

change water to combat nitrate poisoning

Changing the water is the first step in combating nitrate poisoning. Changing out all the water at once is not advised, as it can stress the fish and cause trauma. It is recommended to change 40% of the water on the first day. After that, change 10% of the water each day until you achieve the optimal nitrate levels.

Use a Filter 

After you have changed the water, it is worth investing in a filter to filter out nitrates and keep the nitrate levels in your tank low. Some filters use bacteria in the water to consume nitrate while others use materials that absorb nitrates and remove them from the water.

Last update on 2023-09-21 / Affiliate links / Images from Amazon Product Advertising API

Put Your Fish in a Refugium

A refugium is a second, smaller tank that you keep filled and stable at all times in case you have a sick fish or need to remove a fish from the tank for some reason. If the nitrate levels in your main tank have become dangerously high, move your fish into a refugium until you can stabilize the nitrate levels.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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