Nitrate Control in Fish Tanks: How to Keep Your Aquarium Healthy

If you’re just starting out with your fish care journey or just curious about what goes on in your tank, you may have heard of nitrates. But what exactly are nitrates? Are nitrates safe? What can you do to ensure that nitrates will not harm your tank? In this article, we will discuss the answers to all these exciting questions, and more! So, keep on reading!

What Are Nitrates?

Nitrates are a type of chemical compound that contain nitrogen and oxygen. They’re commonly found in various forms in both natural and man-made environments, including soil, water, air, and even food.

In the context of aquariums and aquatic environments, nitrates play an important role in the nitrogen cycle. This process involves the conversion of harmful ammonia produced by fish waste into less toxic nitrite and, eventually, nitrate, which can be safely removed through regular water changes or absorbed by live plants.

While low levels of nitrates are generally not harmful to fish, high levels can cause health problems and even death. In addition, high nitrate levels can lead to excessive algae growth and other water quality issues in the tank. It’s important for aquarium owners to regularly test their water for nitrates and take steps to keep levels within safe ranges.

Sources of Nitrates

There are several common sources of nitrates in aquariums and aquatic environments:

Fish waste: As fish produce waste (feces and urine), it breaks down into ammonia. Bacteria then convert this ammonia into nitrite and eventually nitrate.

Overfeeding: Feeding your fish excessively can lead to an accumulation of uneaten food that can decompose into ammonia.

Tap water: Depending on where you live, tap water may contain varying amounts of nitrates due to agricultural runoff or other environmental factors.

Decaying plant matter: Dead leaves or other organic material that has fallen to the bottom of your tank can also contribute to nitrate levels over time.

Are Nitrates Safe for Aquariums?

As a loving pet owner, you want to ensure your fish live their best lives in a safe and healthy environment. That’s why it’s important to understand the role of nitrates in your aquarium and whether or not they’re safe for your fish.

So, are nitrates safe for aquariums?

First off, nitrates are a natural part of the nitrogen cycle in an aquarium. They’re produced as a result of the breakdown of ammonia from fish waste and uneaten food. In low levels, nitrates are actually beneficial for plants and can help promote their growth.

However, high levels of nitrates can be harmful to your fish. When nitrate levels exceed 40 ppm (parts per million), they can cause stress to your fish by reducing their ability to absorb oxygen from the water. This can lead to health problems such as fin rot or ich.

Additionally, high nitrate levels can also promote algae growth in your tank, which can compete with your fish for resources and create unsightly green water.

So what should you do if you suspect that your nitrate levels are too high? First, you should regularly check your tank parameters using test kits. You should also perform regular partial water changes (around 20%-30% weekly) to help remove accumulated nitrates from the water.

Another important factor is feeding only what your fish will consume within a few minutes. Overfeeding leads to excess uneaten food that decomposes into ammonia and contributes to high nitrate levels.

It’s important to keep in mind that while nitrates are necessary for plant growth and part of the natural nitrogen cycle in an aquarium, it’s crucial to monitor their levels regularly and take action when they become too high.

Fighting fish, Siamese fish, in a fish tank decorated with pebbles and trees, Black background.

How Much Nitrate Should Be in A Fish Tank?

One important factor in maintaining a healthy fish tank is managing the levels of nitrate in the water. So, how much nitrate should be in a fish tank? 

Ideally, nitrate levels in a fish tank should ideally be kept below 40 ppm (parts per million). At levels above this, nitrate can cause stress to your fish by reducing their ability to absorb oxygen from the water. This can lead to health problems such as fin rot or ich.

It’s important to regularly check your nitrate levels using a test kit and take action if they exceed 40 ppm. One effective way of lowering nitrate levels is by performing regular partial water changes (around 20%-30% weekly) to help remove accumulated nitrates from the water.

Additionally, feeding only what your fish will consume within a few minutes can also help keep nitrate levels under control. Overfeeding leads to excess uneaten food that decomposes into ammonia and contributes to high nitrate levels.

Lastly, it’s also worth noting that some fish species are more sensitive to high nitrate levels than others. For example, goldfish and bettas are particularly sensitive and may require lower nitrate levels than other types of fish.

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How Do You Monitor Nitrate Levels?

As a fish owner, one of the most important things you can do to ensure the health and well-being of your aquatic pets is to monitor the nitrate levels in their environment. Here are three ways to do so:

1. Test Kits

One of the most common ways to monitor nitrate levels in a fish tank is by using test kits. These kits typically use a colorimetric method where you add a chemical reagent to a water sample from your aquarium and compare the resulting color to a chart to determine the nitrate level.

Test kits are readily available at most pet stores and online retailers, and they come in various types that cater to different needs. For example, some test kits are designed for freshwater tanks, while others are for saltwater tanks.

2. Electronic Testers

Electronic testers provide another option for monitoring nitrate levels in your aquarium. These devices use sensors to measure the nitrate concentration in your aquarium water and display it on a digital screen.

Electronic testers can be more expensive than test kits, but they offer greater precision and convenience since they don’t require any color comparison or interpretation.

3. Aquarium Controllers

Advanced aquarium controllers can also monitor nitrate levels along with other parameters such as temperature, pH, and salinity. These controllers typically require more setup and maintenance than test kits or electronic testers but can provide more comprehensive monitoring of your aquarium environment.

Aquarium controllers usually come with multiple probes that need calibration every few months or so. They can be programmed to alert you when certain parameters go outside preset ranges, making them particularly useful if you have many tanks or want remote monitoring capabilities.

What Causes High Nitrates in Aquariums?

If you’re a fish keeper, you know how important it is to maintain good water quality in your aquarium. High nitrate levels can be a common problem in aquariums, leading to health problems for your fish and other aquatic inhabitants. But what causes high nitrates in aquariums?

The Nitrogen Cycle

To understand what causes high nitrates in aquariums, it’s essential to understand the nitrogen cycle. In the aquarium, the nitrogen cycle is the process by which beneficial bacteria convert fish waste and uneaten food into less harmful substances.

The nitrogen cycle begins with ammonia, which is produced by fish waste and uneaten food. Beneficial bacteria in the aquarium, primarily Nitrosomonas and Nitrobacter, convert ammonia into nitrite and then into nitrate. Nitrate is less harmful than ammonia and nitrite, but high levels of nitrate can still be harmful to fish and other aquatic life.


One of the most common causes of high nitrates in aquariums is overfeeding. When you feed your fish more food than they can eat, the excess food will decompose, producing ammonia. Ammonia is the starting point for the nitrogen cycle, and if there is too much ammonia, it can lead to high nitrate levels.

To avoid overfeeding, ensure you’re feeding your fish the appropriate amount of food for their size and species. You can also use feeding rings or automatic feeders to control the amount of food that is dispensed.

Infrequent Water Changes

Another common cause of high nitrates in aquariums is infrequent water changes. Over time, nitrates can accumulate in the aquarium water, and if they are not removed through water changes, they can reach high levels.

To avoid high nitrate levels, perform regular water changes. The frequency of water changes will depend on the size of your aquarium and the number of fish you have. As a general rule, a 25% water change every two weeks is recommended for most aquariums.


Overcrowding is another cause of high nitrate levels in aquariums. When there are too many fish in the aquarium, the amount of waste they produce can exceed the capacity of the nitrogen cycle. This can lead to high ammonia and nitrate levels.

To avoid overcrowding, ensure you’re not keeping too many fish in your aquarium. Follow the recommended stocking levels for your aquarium size and species of fish.

What Does High Nitrates Do to Dish?

When there are high levels of nitrates in the water, it can cause a lot of problems for fish and other aquatic creatures. Here are some of the things that can happen:

Stunted Growth

Fish need a healthy environment to grow properly, but when there’s too much nitrate in the water, it can hinder their growth and development. This means they might end up smaller or underdeveloped.

Poor Health

Fish living in water with lots of nitrates may become more vulnerable to diseases and infections. Elevated nitrate levels weaken their immune systems, making them more likely to get sick.

Reproduction Issues

High nitrate levels can also interfere with fish reproduction. They might not spawn as much or at all if there’s too much nitrate in the water.

Strange Behavior

Fish living in water with high nitrates may act strangely. They might be lethargic or hyperactive, which isn’t typical for their species.


If nitrate levels get too high, it can even lead to fish dying suddenly or over time due to stress on their organs and systems.

To prevent these problems, ensure you keep your aquarium’s nitrate levels within safe limits by doing regular water changes, maintaining proper filtration, avoiding overfeeding, and not overcrowding the tank. Testing the water regularly is also important to ensure everything stays healthy for your aquatic pets.

How Do You Lower the Nitrates in Your Aquarium?

High levels of nitrates can be harmful to your aquarium’s inhabitants. Here are some effective ways to lower nitrate levels:

Perform Water Changes

One of the easiest and most effective ways to reduce nitrates in your aquarium is by performing regular water changes. This will dilute the concentration of nitrates in the water.

Use Live Plants

Live plants are a great way to absorb excess nutrients, including nitrates, from the water. They act as natural filters and help keep the water clean.

Adjust Feeding Habits

Overfeeding your fish can lead to excess waste, increasing nitrate levels. Adjust feeding habits and avoid overfeeding your fish to keep nitrate levels under control.

Increase Filtration

Increasing filtration can help remove excess waste and debris from the water, which will reduce nitrate levels. Consider adding an additional filter or upgrading your current one for better performance.

Use Nitrate-Reducing Bacteria

Nitrate-reducing bacteria can help to lower nitrate levels in your aquarium by converting nitrates into nitrogen gas, which is then released into the air. You can introduce these bacteria into your tank using products like “bio balls” or “live sand” containing the bacteria.

Use Chemical Filtration Media

Chemical filtration media, such as activated carbon or zeolite, can absorb excess nutrients from the water, including nitrates.

Use a Protein Skimmer

A protein skimmer is a device that removes organic waste from the water before it can break down into nitrates. By removing the waste before it can contribute to nitrate levels, you can help to keep nitrates under control.

How Do You Remove Nitrates from Water Naturally?

If you have high nitrate levels in your water, there are natural ways to remove them. Here are some effective methods:

Use Plants

Aquatic plants, such as duckweed, hornwort, and water lettuce, can help remove nitrates from the water naturally. These plants absorb nitrates as a nutrient source and use them to grow.

Increase Aeration

Increasing aeration in the water can help promote the growth of beneficial bacteria that break down nitrates. This can be done by adding an air stone or increasing the flow rate of your filter.

Add Zeolite

Zeolite is a natural mineral that can absorb excess nutrients from the water, including nitrates. It works by exchanging its ions with those of the dissolved nutrients.

Use Biofilters

Biofilters contain beneficial bacteria that break down organic matter in the water, including nitrates. They can be added to your aquarium’s filtration system or used separately.

Perform Water Changes

Performing regular water changes will dilute the concentration of nitrates in the water and remove excess waste and debris.

Avoid Overfeeding

Overfeeding fish can lead to excess waste and debris in the aquarium, which increases nitrate levels. Avoid overfeeding and only provide enough food for your fish to consume within a few minutes.

What Water Filters Remove Nitrates?

If you have high nitrate levels in your water, a water filter can help remove them. Here are some types of filters that are effective at removing nitrates:

Reverse Osmosis Filters

Reverse osmosis filters use a semi-permeable membrane to remove impurities from the water, including nitrates. They work by forcing the water through the membrane and trapping the impurities on one side.

Ion Exchange Filters

Ion exchange filters use resin beads to exchange ions with those of dissolved impurities, including nitrates. The beads attract and trap the impurities, removing them from the water.

Distillation Filters

Distillation filters work by heating the water to create steam, which is then condensed back into liquid form. This process removes impurities, including nitrates, from the water.

Activated Carbon Filters

Activated carbon filters use a porous carbon material to absorb impurities from the water as it passes through. This includes nitrates, which are attracted to the surface of the carbon material.

Catalytic Carbon Filters

Catalytic carbon filters use activated carbon with a specialized catalyst to break down organic matter in the water, including nitrates.

When selecting a filter for nitrate removal, be sure to check its specifications and ensure that it is designed for this purpose. Regular maintenance and replacement of filter media is also important for ensuring continued effectiveness.

Nitrate Control in Fish Tanks_ How to Keep Your Aquarium Healthy


Is Fish Poop a Good Enough Fertilizer for Aquarium Plants?

Fish poop can be a good fertilizer for aquarium plants as it contains essential nutrients like nitrogen and phosphorus. However, relying solely on fish waste may not provide enough nutrients for all types of plants. It’s best to use fish poop with other fertilizers and closely monitor nitrate levels to avoid harming your plants and fish.


In conclusion, nitrate levels in fish tanks are an important factor to monitor for the health and well-being of your aquatic pets. High nitrate levels can lead to various issues, including poor water quality, algae growth, and stress or illness in your fish. However, by implementing regular maintenance practices such as water changes and using natural methods or filters to remove nitrates from the water, you can ensure a healthy environment for your fish to thrive in. Remember to regularly test your water for nitrate levels and take action if necessary.

With proper care and attention, you can enjoy a beautiful, vibrant aquarium that brings joy and relaxation into your home!

About the author

Hey! I'm Antonio!

Betta fish keeper for over 6 years now! Since owning a betta I've also housed all kinds of tropical fish, and have seen all manner of problems and how to look after them!

If you need any advice you can always message me or better yet join the Facebook group where a community can answer your questions!

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