How To Reduce Ammonia In Fish Tank (11 Step Guide)

by | Articles, Blog, Breeding and Care, Freshwater Fish, Saltwater Fish

The dreaded ammonia spike has a bad rap for good reason: High ammonia levels can slowly suffocate your fish, and eventually kill them. This is referred to as “ammonia poisoning.” Once you figure out that you have ammonia in the tank, it’s critical to act quickly to eliminate it. This guide will go over ammonia basics, what it is, how it works in an aquarium, how to reduce ammonia in a fish tank, and how to prevent spikes. Let’s dive in!


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1. What Is Ammonia?

Ammonia is a chemical compound formed with the help of hydrogen and nitrogen atoms. In a fish tank, ammonia is present in two different forms and both are different from each other.

One is an unionized form, a toxic gas known as free ammonia (NH3). It develops in fish tanks as a result of fish waste, uneaten fish food, dead fish or plants and decayed algae (through the process of decaying organic matter).

The second form is ammonium (NH4+). It’s the ionized form which occurs as a non-poisonous salt. While it’s not as toxic as NH3 is, it’s still not safe for your fish tank. Here’s why: NH4+ is less toxic because it doesn’t affect the gills of fish as quickly as unionized (NH3) ammonia does. This makes it less directly harmful, but it’s still harmful in the long-term because when pH rises, NH4+ can turn into NH3 (toxic ammonia). This is why fish keepers get upset about the presence of NH4+ as well.

Because ammonia is toxic to fish, ammonia levels should always be at 0. But technically speaking, ammonia still occurs in fish tanks even when the levels are kept at 0. How is this possible?

This is what’s referred to as a “controlled level” of ammonia. It means that ammonia that is released into the tank is instantly taken in by plants for their growth. In fact, plants actually benefit from ammonia. In this way, we can say that a controlled level of ammonia is acceptable in a fish tank – While also understanding that the ammonia levels should always remain at 0.

In order to determine ammonia levels, fish keepers use a test kit. Water testing should be performed regularly (at least on a weekly basis) to make sure that the ammonia in a fish tank never exceeds the controlled level, as otherwise, it can be dangerous for the lives of the fish.

2. What is the Aquarium Nitrogen Cycle?

The aquarium nitrogen cycle is the process by which ammonia is converted into nitrates, and a tank’s beneficial bacteria become balanced enough to support aquatic life. All aquarium tanks need to be cycled properly before adding fish; If not, the fish will die. Beneficial bacteria colonies help to reduce ammonia and nitrite levels to 0 ppm.

Here are the three phases of the aquarium nitrogen cycle in detail:

● Microorganisms and fish eating their food produce fish waste, which is called ammonia (NH3).

● ​Plants and beneficial bacteria “eat” this fish waste, which helps them grow. After “eating” ammonia (NH3) these beneficial bacteria will release ammonia in the form of nitrite (NO2-). This is the process of conversion of ammonia into nitrite.

● ​Beneficial bacteria (Nitrobacter) “eat” nitrite and as a result, they produce nitrates (NO3-). These nitrates are used by the plants in a fish tank (when at a controlled level).

It’s important to keep an eye on nitrate levels. If they’re too high, they can hurt fish and aquatic plants. Nitrate levels should range from 0.5 to 5.0 ppm at the most.

There are two primary types of beneficial bacteria involved in this process: The first is Nitrosomonas and the second is Nitrobector. Beneficial bacteria grows naturally on items in the tank like substrates, filters, rocks, pumps and decorative aquatic items.



Nitrogen cycle graphic

Ammonia (NH3)  >> Nitrite (NO2-)  >> Nitrate (NO3-) >> Plants & Water Changes

3. What Does Ammonia (NH3) Do in Aquariums?


Ammonia (NH3) is a naturally occurring chemical byproduct that should always be at controlled levels (eg, 0 ppm) in a fish tank; In a healthy, cycled tank, the plants benefit from and help absorb ammonia byproduct from fish waste, and tank maintenance measures (such as water changes) also keep it in check.

A controlled level of ammonia helps aquatic plants and healthy bacteria to grow. The key is that it must be controlled. In other words, there should never be ammonia in the tank because it’s immediately taken in by plants and and/or mitigated by a healthy tank with good maintenance.

Ammonia in a fish tank is toxic for fish because it suffocates them; If the levels are high enough, they will be unable to breathe, and will die.

Foul odor in a fish tank is a good indication that ammonia is present. This is dangerous for your fish and you should correct it right away.

To prevent your tank from getting to that point, use a test kit regularly (at least once a week, depending on the tank size, filtration, etc.) to ensure there is no ammonia in the tank.

4. What Ammonia Levels Are Acceptable in Your Aquarium?


Ammonia is highly dangerous for fish gills and their organs, and at the end of the day, no ammonia should be present in your tank. Keep ammonia levels at 0 ppm to keep your fish healthy.

5. How Do You Test for Ammonia?


The best way to test for ammonia is to use a test kit, which you can buy online or at your local aquarium store.

It’s also a good idea to observe your fish; If your fish is stressed, lethargic, suffering from redness around the gills, and/or there is a smell in the aquarium, these are good indications that you have uncontrolled ammonia in your tank.

6. What Happens If Your Ammonia Levels Are Too High?


A rise in ammonia levels is alarming, because it damages fish gills, organs, and tissues (eg, ammonia poisoning). Ammonia slowly suffocates your fish, puts them under stress, and stunts their growth. It can affect everything from their reproductive systems to coloring. Ammonia can and will eventually kill a fish.

7. What Causes Ammonia in Fish Tanks


An ammonia problem in a fish tank can be caused by several different things, and sometimes a combination of them. To keep your ammonia levels at 0 ppm, you’ll want to keep an eye on the factors listed below. Here are some of the most common culprits of ammonia:

7.1 Die-off


To avoid ammonia poisoning, you should be on alert for any die-off of plants or leaves and remove them immediately, as they can raise ammonia levels. Die-offs sometimes happen when you move aquarium plants from one tank to another. Similarly, changes in tank water quality and exposure to air for longer periods can result in die-off.



Pruning old leaves


Dead fish is another factor in increased ammonia levels. When a dead fish start to decay, it generates ammonia.

Long story short: Whenever something dies in the tank, remove it right away.

7.2 Overfeeding


Overfeeding can cause ammonia problems for two reasons:

1) As much as your fish eats, it produces fish waste in the same quantity (which fuels ammonia levels).

2) When overfed, fish can leave uneaten food that will decompose as decaying organic matter which, after some time, can build up ammonia in fish tanks.

To avoid this, feed your fish regularly but in small quantities. Use an automatic feeder if needed, to avoid dumping a bunch of food in the tank before you leave for work for the day, for example.

It’s worth noting that uneaten food can also stick in between aquarium decor, fueling ammonia that way too.

7.3 Overcrowding/Overstocking


Keeping too many fish in a tank (also known as “overstocking”) can cause ammonia problems. The more fish you have in your tank, the more poop, biowaste, etc they’ll make. Fish need enough space and a tank can only accommodate so much diffusion and filtration. Overstocking = too many fish. This is bad not only for ammonia reasons, but for fish health and well-being in general.

7.4 Poor Fish Tank Maintenance


Poor fish tank maintenance can be a major culprit of ammonia. If you skip or delay maintenance, ammonia levels can rise. An inadequate filtration system or a filter that’s not properly sized to the tank can also be a problem here. Aquarium cleanliness is a major factor in ensuring fish health, a balanced tank, and 0 ppm ammonia. Use a high quality filter, perform regular weekly water changes, and don’t skip maintenance.

7.5 Drastic Water Changes and/or Low Amount of Beneficial Bacteria


A higher amount of good bacteria in your aquarium means lower ammonia levels. Keeping a healthy amount of beneficial bacteria is crucial. An unfortunately common problem for novice aquarists is performing water changes that are too large: A cycled, healthy tank is an intricate ecosystem that contains good bacteria that will fight to keep a tank balanced. This bacteria lives in various areas of the tank, from the water itself to the filter. When you remove a ton of the tank water all at once, you also remove the good bacteria that helped keep toxic ammonia at bay. Removing the good bacteria means ammonia can spike and kill your fish. This is why fish sometimes die after a drastic water change.

It’s always better to do frequent, smaller water changes than larger, less frequent ones.

7.6 Increased pH Level


Increased pH causes increased ammonia. PH above 9 is dangerous for your fish and can kill them quickly.

7.7 New Fish Tank


Adding fish to a new tank without cycling the tank first is a disaster that can result in large fish die-offs. A new tank needs to “live” for a while first without fish in it, so it can cycle and develop good bacteria, which keeps ammonia under control.

These beneficial bacteria will then be able to fight the ammonia produced by fish waste, and give fish a healthy environment in the aquarium. A tank that hasn’t been cycled yet doesn’t have that good bacteria to remove ammonia.

8. What Are Signs of Ammonia in the Fish Tank?


Ammonia is a major killer of aquarium fish. While regular testing is the best way to be 100% sure that your ammonia levels are at 0 ppm, there are also some telltale signs of increased ammonia that you should keep an eye out for:

8.1 Odors


A stinky smell in your aquarium reflects increased ammonia. Kind of like a cat pee smell. Not pleasant.

Depending on how bad the ammonia problem is, the smell can be very strong and difficult to remove until ammonia levels are under control.

8.2 Lethargy


Ammonia damages the organs inside the fish’s body, and slows them down significantly, resulting in symptoms like decreased appetite and laying at the bottom of the tank. The fish will not be as active as before.

8.3 Gasping for Air


Ammonia affects the oxygen levels of the tank and makes it difficult for fish to breathe. This results in suffocation, so fish will start coming up to the surface to gasp for oxygen since they can’t get it from the aquarium water.

Another way ammonia creates breathing problems for fish is that it causes gills and other organ problems. To help themselves breathe, they’ll come to the surface since they can’t get enough oxygen in the water.

8.4 Redness Around Gills


Some fish are hardier than others; Some will succumb quickly to increased ammonia, and others will take longer. For hardier fish, they may not show any other symptoms but redness around their gills. This redness is the result of burning gills or other organs.

If you don’t control ammonia levels, then this redness will increase into a severe infection.

8.5 Fish Behavior


As you can imagine, increased ammonia levels impacts fish behavior. It affects their gills, fins, organs, skin and even skin color. These effects can change your fish’s behavior. They may be less active, lose their coloring, eat less, swim more slowly, and generally lose energy. Sometimes when suffocated a fish may try to stay on the edge of the aquarium to inhale oxygen, or other areas that make it more convenient to breathe.

9. How Can I Get Rid of Ammonia? (In 11 Easy Steps)



Cleaning/water change



If your fish tank is affected by ammonia, it’s crucial to get rid of it ASAP in order to keep your fish alive and healthy. Depending on how bad your ammonia problem is, you might benefit from a combination approach. A very serious ammonia issue may, for example, require Seachem Prime + 50% daily water changes until the ammonia levels are back at 0.

Just be sure to test after every change you make, so you can track how it impacts your tank. Here are ways to lower ammonia:

9.1 Water Changes (Recommended)


One of the best ways to remove ammonia and improve water quality is through partial water changes. If you have an ammonia problem, I recommend performing partial water changes every 24 hours until you reach 0 ppm ammonia.

Test your water first, and record the readings for reference later. If you have increased ammonia, change 50% of the water on the first day. Test again and record. Repeat the same process on the second day; If the ammonia level is still high, then do a change of 20-30% water. Keep repeating the process until you reach your desired results, 0 ppm.

In severe cases, you might have to do up to a 50% water change daily until you’re able to get your ammonia levels to 0.

Water changes are a very effective and budget-friendly method to reduce and remove ammonia.

9.2 Ammonia Remover (Chemical Supplement)


Sometimes, you need a solution fast. While chemical supplements aren’t a long-term solution (more on that in a moment) they can help you in a time of need when it’s absolutely critical to lower ammonia right away.

These include products such as Fluval Ammonia Remover and Seachem Prime. They’re effective and can be helpful in the short term.

For a long-term solution, focus on diagnosing the reasons for the ammonia increase. From overfeeding to overcrowding or lack of proper maintenance, there are many things that can cause the problem. Once you’ve figured our what it is, you can remedy it.

9.3 Water Conditioners



Adding water conditioner



Water conditioners help detoxify a tank from ammonia; it’s not a fast-working method, but it helps reduce ammonia, nitrite, and chlorine in the fish tank. This method will take some time to remove ammonia from the tank.

9.4 Beneficial Bacteria


Beneficial bacteria helps reduce ammonia levels in your fish tank. If your ammonia problem is in a new aquarium, you can add gravel substrate from a healthy, established tank to add beneficial bacteria to yours. This is because they live in the substrate.

You can also use the filter pad of an old aquarium – Another spot where beneficial bacteria live. This is a good way to help buffer a new tank against ammonia, too.

Finally, there are bottled bacteria available that you can purchase online or at your local aquarium store.

9.5 Lowering Water pH


High pH can contribute to increased ammonia. Some substrate, such as coral sand, can be culprits. If pH exceeds 7, it’ll cause an ammonia increase. If pH reaches 9, it can kill your fish.

A chemical pH adjuster can work well in reducing the pH level of water. A partial water change can also help lower the pH level.

Other methods of lowering pH include adding driftwood (boiled beforehand of course), adding aquarium-safe peat moss, and CO2 are other ways to help lower pH.

9.6 Increasing Biological Filtration


Biological filtration is a component of the nitrogen cycle of an aquarium in which beneficial bacteria absorb harmful ammonia, creating a healthy environment for fish. Biological filtration media enhances the growth of beneficial bacteria, lowering ammonia levels.

To increase biological filtration, you can use porous media, live rock, Bio-Home Ultimate Media and MarinePure (a substrate for biological filtration).

9.7 Upgrading Your Filtration System


Filters play an important role in the aquarium. Whether you’re a beginner or an experienced aquarist, you should have a high-quality filter in your aquarium; Filters not only help in removing ammonia and other toxins from your fish tank, but also assist beneficial bacteria. These beneficial bacteria help provide a quality environment for fish.

If you’ve already fixed a filter in your aquarium but still not getting the desired results, then go for two things.

If you already have a filter but are still having trouble, check to see if it needs to be cleaned or if there’s any blockage in it. In some cases, you may even need to add a second filter. Just be mindful of their water flow when selecting one, especially if you have fish that need slow-flowing water, like betta.

9.8 Add Freshwater Fish Tank Plants


Live plants are an excellent biological filter. They take in harmful gasses for their own growth, and release oxygen in return. They make a strong contribution to water quality and can absorb ammonia and other compounds toxic to fish.

9.9 Add Porous Dry Rock to The Freshwater Aquarium


Adding dry rock to a freshwater aquarium can help combat ammonia. Black lava rock is a great example. This works slowly, and I definitely wouldn’t turn to it for an ammonia emergency. Researchers have found that the effect it has is small.

The downside is that these rocks can have sharp edges and corners that can injure fish.

9.10 Add Live/Dry Rock to Saltwater Fish Tank


This one is specific to saltwater aquariums, but it’s similar to the dry rock example above. Live rock is a rock that consists of dead corals and several other organisms. When placed in a saltwater aquarium, it produces a large variety of bacteria and algae that work as biological filters for saltwater aquariums.

All these organisms fight ammonia and other harmful gasses in a saltwater fish tank. Live rock can also give a helpful boost to the nitrogen cycle in an aquarium.

9.11 Cycling Tank


This one should go without saying, but we still need to say it: Tanks need to be cycled properly before you add fish to them. A new tank is more prone to increased ammonia because there’s less beneficial bacteria present as it’s not yet an established tank. Less beneficial bacteria means higher likelihood of ammonia. Cycle your tank to support healthy bacteria.

10. How to Prevent an Ammonia Spike



Water testing



When ammonia levels rise suddenly, it’s known as an “ammonia spike.” The most common culprits of ammonia spikes include new tank syndrome/not cycling a tank, overstocking, overfeeding, and poor tank maintenance.

That said, you might have an ammonia spike and not know what it is right away. It might take time to figure it out. I knew of someone who had a terrible ammonia spike and couldn’t figure out what had caused it, until he discovered his kids had added some algae remover (too much!) to the tank. Nevertheless, work to lower the ammonia levels ASAP.

When stocking your tank or adding livestock to an established tank, don’t add a bunch of fish at once. Instead, add one species at a time, then test water parameters and monitor the water to see how the new addition affects the tank before adding more.

Perform weekly water changes and schedule maintenance so you don’t miss any. Avoid overfeeding, and feed in small quantities regularly. Add live plants and driftwood, and keep a clean tank! Remove any dead or decaying matter right away.

11. FAQ

11.1 Does Ammonia Remover Work?


Yes, ammonia remover will work, but it’s a short-term solution. In the long-term, you’ll want to figure out what caused the ammonia.

11.2 How Do I Lower Ammonia in My Fish Tank With No Water Change?


Truth is, the best way to lower ammonia in a fish tank is to do partial water changes. In fact, sometimes it’s the only way, especially in more severe cases. I think it’s worth reiterating here that ammonia is deadly to fish, and it slowly suffocates, burns, and kills them. If you’re keeping fish, it comes with responsibility to them to keep their environment clean and healthy. This includes water changes when needed. They’re vulnerable and depend on you.

Keeping a clean tank, having adequate filtration and adding live plants can help, but they’re not a substitute for water changes when they’re needed.

11.3 What Causes High Ammonia Levels in a Fish Tank?


There’re always several reasons behind the increase in ammonia levels. This includes:

● New tank syndrome/not cycling a tank

● Dead fish and plants

● Overfeeding your fish

● Overcrowding/Overstocking

● Poor fish tank maintenance

● Drastic water changes and/or Low amount of beneficial bacteria

● High pH level

11.4 What Breaks Down Ammonia in a Fish Tank?


Filters, live plants, biological media filters and chemical supplements all break down ammonia in a fish tank. However, a partial water change actually removes it.

Want more? Watch Aquarium Co-op break it down, beginner-style, below:

12 Conclusion


Ammonia is an alarming and deadly compound to find in your fish tank. If you don’t treat it right away, it will slowly suffocate and kill your fish. There’s a wide range of things that can cause it, from overfeeding to poor maintenance and high pH levels. The most common culprits are not cycling a new tank properly. Drastic water changes can similarly cause ammonia spikes. Work through the items on this list until you determine the cause of the increased ammonia. Perform partial water changes daily, testing in between, until the ammonia is back at 0 ppm. When in doubt, consult your local aquarium store for help. Online forums can also be really helpful. Last tip: Avoid big box stores as they’re less likely to have fish keepers there. Good luck!




Additional Sources/Resources/Reading




To say that I’m obsessed with all things saltwater is a bit of an understatement. Aquarium Passion has served freshwater and saltwater aquarium hobbyists for over 10 years, and I'm committed to keeping the information accurate and free. My post-bac certification in Sustainability informs my writing about aquarium conservation efforts. When I'm not writing at AP, I'm out in the ocean or researching weird fish.


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