Ammonia In Fish Tank (The Complete Guide)

Ammonia is a natural chemical that exists in most fish tanks and is safe in small amounts but can quickly build up and become dangerous. If ammonia is left to build up, fish can be seriously harmed and even killed, so preventing excessive ammonia levels is critical for maintaining the health and welfare of fish.

In the following article, we look at everything you need to know about the harms of ammonia in your fish tank, including important information on how to prevent and remove excessive ammonia. Read on to find out more about how to protect your fish from ammonia. 

Signs Of Ammonia In Your Fish Tank

Your Fish Is Experiencing Weakness or Lethargy

Ammonia can cause your fish to have much less energy than usual, making them appear more lethargic than you might expect. Your fish may also appear to become tired after the smallest movements. Look out for signs of weakness and lethargy, including less movement or more sleeping.

You Notice Inflammation of the Fish’s Body

When your fish is exposed to too much ammonia, the effects can cause parts of the body to become inflamed. This usually affects the fins or gills, although other areas like the eyes and anus may also become affected. Be sure to be on the lookout for any signs of inflammation in the body.

You Fish Is Staying at the Bottom of the Tank

Ammonia can cause your fish to become so weak they are unable to swim or have difficulty being able to breathe, which can cause them to spend most of their time lying on the bottom of the tank. For surface-dwelling fish, in particular, this is usually a sign of excessive ammonia levels.

You Notice Your Fish Gasping for Air

If your fish begins to gasp for air at the surface of the water and seems to have difficulties breathing underwater, you need to check ammonia levels. This is your fish attempting to gain access to fresh air and is usually a sign that there is too much ammonia in the water, which is affecting the fish’s breathing.

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Your Fish Experiences Physical Changes to the Body

Ammonia can cause physical effects on the body, such as bleeding, changes in color, or torn fins. These changes usually occur as a result of burns caused by ammonia and can be very painful for your fish to experience. Check your fish regularly for signs that their body is changing in any way, as it could be due to ammonia levels.

You Notice Red Streaks on the Fish’s Fins

Red streaks appearing on the fish usually indicate that the fin has begun to rot, which is very common in fish living in water affected by high ammonia levels. It may appear as though your fish is bleeding across its body, so you should be on the lookout for signs of this and check ammonia levels.

Your Fish Has a Loss of Appetite

As ammonia levels begin to rise, your fish will become more lethargic, and their body will begin to fail. This can cause them to eat less due to a loss of appetite, which can cause them to become even weaker. Keep a close eye on how much your fish is eating, as this may help you spot if there is too much ammonia in the water.

What is Ammonia?

Ammonia is a natural chemical that builds up in aquarium tanks as a result of life in your fish tank. It comes from a build-up of the waste produced by your fish and the things they eat. Ammonia in small amounts is not always bad and is even used by plants in your tank as fertilizer to aid in their growth.

However, if ammonia is left to build up, it can be dangerous to your fish and cause problems for other living things in your tank. Ammonia can prove fatal to fish when levels get too high. Your fish can seriously suffer from too much ammonia, so it’s vital to check levels frequently.

What Causes Ammonia In Fish Tanks?

Waste Produced or Left Behind by Fish

The biggest cause of ammonia in a fish tank is a build-up of the natural waste your fish produces every day. Although some ammonia is produced through the release of feces or urine, most of the ammonia in fish tanks is created through ammonia released through the gills.

Too Many Fish in the Tank

As a result of fish producing ammonia naturally, overstocking your tank with too many fish can lead to an excess of ammonia. This is especially the case with a tank that hasn’t yet completed the nitrogen cycle, meaning it isn’t equipped to deal with so many fish producing ammonia at once.

Fish Being Given Too Much Food

Fish food quickly disintegrates, leaving behind ammonia as it rots and decays. If you provide your fish with more food than they can eat, the amount of ammonia in the water can very quickly build up to dangerous levels, which can be very harmful to your fish and plants. Removing leftover food or limiting how much you are giving can massively control ammonia.

Rapid Changes to Water

Any rapid change to the water can cause ammonia levels to rise as a reaction to said changes, particularly when these changes are the result of different types of water. Adding new chemicals like chloramine can cause ammonia levels to rise to dangerous levels very easily.

The Use of Untreated Tap Water

Untreated tap water can contain levels of ammonia which may start off small but can quickly build up to excessive, dangerous amounts. Continuous use of untreated water in your tank means ammonia may be constantly being added to the tank, allowing it to build up over time.

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How To Check Ammonia Levels In Fish Tank

Use an Ammonia Test Strip Kit

It’s recommended that an ammonia test is completed once a week to ensure levels are not allowed to build up. You can also perform a test whenever you see signs of sickness in fish or lose a fish for any reason you aren’t sure of. A test strip kit provides the quickest results and is relatively easy to complete.

Use a Salicylate Ammonia Test

Another test you can perform to check ammonia levels is a salicylate ammonia test, which involves adding chemicals to a water sample to determine how much ammonia is present. These tests are thought to provide more accurate results than a test strip kit. You can repeat the test a few times to ensure ammonia levels are improving.

Use an All-Round Test Kit

Most aquarium tests are able to test for anything potentially dangerous in your tank and water, such as high nitrate levels and other harmful chemicals. Completing one of these tests can let you know whether there is too much ammonia in your water, as well as any other dangerous chemicals that could harm your fish. 

Check for Smells

Ammonia has quite a particular smell, so you should be able to pick up on it. If your fish tank has developed a strange smell, test your water straight away to check for increased ammonia levels. The smell of ammonia will get stronger the higher the level in your tank is, but smaller amounts can also be detected through scent.

Check Your Filter

An indirect way to check for ammonia in your tank is to check the filter. You should be making sure to check your filter regularly to ensure it is working the way it should be to protect your tank and water from anything harmful. If it isn’t, it may be contributing to ammonia levels in the tank.

What Happens If Ammonia Levels Are Too High?

Fish Can Die

Ammonia essentially poisons your fish, causing damage to its brains and organs. The higher the level of ammonia in the water, the more difficult it is for the fish to expel it from their bodies. Eventually, this will lead to the fish dying, which can be a very painful and stressful death.

Fish Can Be Seriously Harmed

If a fish is not killed by ammonia, it can instead be left seriously injured. Ammonia can cause burns to the gills, which can lead the fish to suffer physical effects for a long time. This can be very painful for a fish to go through and can create further severe stress both physically and mentally. 

Fish Can Become Very Stressed

Some fish can tolerate higher ammonia levels but can still suffer the effects. These fish may not become ill or die from high ammonia levels but may instead become extremely stressed. This can cause them to become vulnerable to developing certain diseases, experiencing color loss, or growing less.

Plants Can Suffer Too

It’s not just your fish that can suffer as a result of elevated ammonia levels – in fact; you should be keeping an eye on any plants you have in your tank too. Too much ammonia is not good for plants, and most will likely be killed by an excess of ammonia in your water. Aquarium plants absorb ammonia as fertilizer and can easily absorb too much.

Your Fish’s Behaviour May Change

An excess of ammonia in your fish tank may cause your fish to experience changes in behavior. A surface dwelling fish may begin to spend more time at the bottom of the tank, or an energetic fish may suddenly become much more listless. These changes can all happen as a result of elevated ammonia levels in the water.

How Do I Get Rid Of Ammonia In My Fish Tank?

Complete a ‘Deep’ Water Change

Doing a ‘deep’ change of the water in your fish tank usually means changing approximately half of the water initially. This is followed by a regular (weekly or biweekly) partial change of around a quarter of the water. Eventually, you should begin to see a significant drop in ammonia levels. 

Remove Any Dead Fish or Plants

Dead and dying fish and plants will eventually begin to decay, which is when they start to let off ammonia back into the water. So it’s important that you remove a dead or dying fish or plant as soon as you notice it, and make sure to test your tank as thoroughly as possible to check for any ammonia already released. 

Reduce How Much You Are Feeding

Overfeeding is one of the key reasons ammonia is produced, as the remaining food is left to rot and eventually releases ammonia. By reducing the amount you are feeding your fish, particularly if you are prone to overfeeding, you can help to reduce the amount of ammonia being released into your tank.

Limit How Many Fish You Have

Fish naturally produce ammonia as a result of biological waste released into the water. So it’s easy for a tank to become overwhelmed by the amount of ammonia continuously being produced when there are too many fish in the tank. By making sure not to overstock on fish, you can help the tank to manage ammonia levels.

Check the Condition of the Filter

Your filter is one of the key parts of managing ammonia levels in your fish tank, so it’s important that you check it regularly. Blockages to your filter can prevent it from doing its job and cause ammonia to build up. Make sure it’s as clean as possible and changed regularly so that it can continue to do its job properly.

Vacuum the Substrate Regularly

The substrate of your aquarium can hold a lot of ammonia-producing impurities, so consider vacuuming it to remove anything that shouldn’t be there. Leftover food or waste can easily become trapped in the substrate, and you should remove this regularly to prevent ammonia from being produced. 

Consider Deep Cleaning Your Tank

As well as cleaning your water out, you should consider deep cleaning your tank itself. Cleaning the tank’s walls and floor can be a big undertaking, particularly if you have a number of fish, but it can work to remove any leftover traces of ammonia once you have cleared it from the water.

How To Prevent Ammonia In Fish Tank

Add Aquarium Plants

Aquarium plants do a great job of managing ammonia levels in your tank, so adding them can help to prevent an excessive amount of build-up. Plants will absorb and use the leftover food and waste your fish produces (and the ammonia released) and convert it to fertilizer to aid in their own growth.

Protect Beneficial Bacteria

Beneficial bacteria is a great way to protect your tank from ammonia, plus a number of other dangerous things. Good bacteria are most likely to grow in your filter and on the substrate of the tank, so protecting these areas will help to prevent ammonia from developing in excessive amounts.

Remove Waste Regularly

Waste from your fish, like biological waste and leftover food, should be removed immediately to prevent ammonia from developing when these things decay and rot. Making sure to stay on top of waste removal is a great way to prevent excessive levels of ammonia in your tank.

Limit the Number of Fish You Have

Overstocking of fish naturally produces an increased amount of ammonia in your tank. So, it makes sense that limiting the number of fish you have at one time will help to prevent ammonia from building up in the tank. The number of fish your tank can handle will depend on the tank itself, but limiting the number will help to prevent ammonia buildup.

Improve Filtration

Filtration that isn’t up to standard can cause ammonia levels to rise in your tank. Your filter is one of the most important parts of ensuring ammonia levels are managed in your water. To prevent ammonia levels from becoming excessive, consider changing out your filter for an improved one or adding an additional filter to increase the flow of water.

Check Your Filter Regularly

Your filter can be a huge cause of rising ammonia levels in your tank, so make sure to keep it as clean and healthy as possible. Not only will this help to maintain ammonia levels in your water, but it will also help you to protect the overall health and welfare of your fish and the tank.


As we have seen, ammonia can be beneficial in very small amounts. However, in excessive amounts, ammonia can be very harmful and even fatal to fish and plants living in a tank. High ammonia levels can cause fish to become extremely stressed, develop diseases, and even die eventually. 

Fortunately, there are a number of ways you can help to prevent ammonia from building up in your tank, including cleaning waste, improving filtration, and limiting how much you feed your fish. Although ammonia can be dangerous to your fish, fortunately, high levels can be dealt with, and you can prevent your fish from having to suffer as a result.

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!