How to Lower Ammonia in a Fish Tank: Pro Advice

Jennifer Doll

Jennifer Doll


how to lower ammonia in a fish tank

Sharing is caring!

One of the aquarium health issues that we address most frequently at Aquariadise is ammonia poisoning. Even at low levels, ammonia and nitrites are incredibly toxic to fish, and should be kept at zero at all times.

Thankfully, with a bit of biological know-how, you can create a healthy nitrogen cycle within your tank to keep water conditions healthy and ammonia-free.

Here, we’ll share how.

Key Takeaways

  • Ammonia is extremely toxic to fish but can be kept at safe levels by fostering beneficial bacteria to convert it to less toxic nitrates via the ‘nitrogen cycle’.
  • If the nitrogen cycle fails, ‘ammonia spikes’ can quickly become fatal. An urgent response is critical to save your fish’s lives.
  • A healthy nitrogen cycle can be maintained by regular tank cleaning, avoiding overfeeding, and maintaining an efficient aquarium filter.

What Is Ammonia?

Ammonia (NH3) is a chemical compound that is produced by decaying organic matter such as dead plants, decaying detritus and algae, leftover food, and fish waste in the aquarium.

At high levels, ammonia poisoning can quickly set in and affect all the organisms in your aquarium. Because of this, it is important to fully cycle a new fish tank and establish a biological filter.

The Aquarium Nitrogen Cycle

The aquarium nitrogen cycle consists of two stages: First ammonia is turned into nitrite that is then turned into nitrate by beneficial bacteria colonies populating the aquarium.

In a new tank, a source of ammonia is needed to jumpstart the cycle. Various aquarium-specific products may be used to dose ammonia or pure ammonia may be added. Otherwise, another popular method is to ‘ghost feed’ which essentially allows uneaten food to decay and release ammonia.

Nitrifying bacteria will then perform nitrification which converts this ammonia to nitrites (NO2). These nitrites are then converted by another type of nitrifying bacteria into nitrates (NO3) which can be more easily taken up by live plants and other organisms.

While nitrate is also toxic in large doses, it is safe for most fish at concentrations below 0.20ppm

What Does Ammonia Do in the Aquarium?

While ammonia might immediately seem like a bad thing to have in the aquarium, it is food for many microorganisms and plants.

Once the fish tank has been cycled, ammonia enters the system by way of fish waste, uneaten food, and decaying organic matter. This then needs to be converted by the good bacteria in your fish tank.

In return, this bacteria feeds on the ammonia, reducing ammonia levels in your tank and keeping fish from ammonia poisoning. In addition, aquarium plants can readily take up ammonia, nitrite, and nitrate to grow, further lowering nitrogen compound levels throughout the tank.

What causes ammonia in the fish tank?

ammonia in fish tank with goldfish

Now that we know what ammonia is, how does it get into our fish tank systems? There’s usually a clear cause for ammonia levels being in our tanks, but sometimes the cause might be the source water, which we’ll discuss later.

However, the main causes of an ammonia problem stem from organic die-off, overfeeding, overcrowding, or poor fish tank maintenance.


Die-off is one of the biggest factors influencing the ammonia levels in your fish tank. Organic matter starts to decay and rot, which can lead to an overload of nutrients flooding the water column, including ammonia.

A dead fish will start to affect water quality after just a few hours. It is important to take count of all your tropical fish and invertebrates daily to make sure that a dead fish doesn’t start to decay in hard-to-reach spaces; all invertebrates should be accounted for as well. There is the chance that, given an efficient cleanup crew, you might not even have time to find the dead fish or invertebrate as the remains have already been consumed otherwise. However, it is still best to remove dead livestock when you see it.

Plants may start to decompose, which can also raise ammonia levels in the tank. While some members of the cleanup crew might be able to handle small plant die-offs, it is usually best to prune the plant before rot sets in and begins to produce ammonia.

If you transfer live filter media or other decor from another fish tank, you will likely experience some die-off; this is how some saltwater fish hobbyists begin their cycle with live rock. Due to changes in water quality and potential exposure to the air for too long, organic material starts to die off during the transfer. This usually leads to a traceable spike in ammonia in the fish tank over the next few days.


Overfeeding can be just as dangerous as having a dead fish left in the tank. More directly, uneaten fish food breaks down and releases nutrients into the water column; uneaten food can also start to rot if left in the fish tank for too long and produce ammonia.

Believe it or not, many fish don’t need to be fed that often; while most hobbyists likely to give their fish 2-3 feedings a day, it’s not entirely necessary, especially if the food is high in protein. More importantly, it is better to give a larger variety of high-quality foods in smaller portions rather than feeding more often with food that has little to no nutritional value.

As a general rule, only feed fish as much as they can eat in a couple of minutes and remove the excess; uneaten food is very likely to get stuck in filter pads, which can easily lead to ammonia leaking into the fish tank.


Similar to overfeeding, overcrowding not only increases the amount of uneaten food entering the system but also the direct waste as a result of having that many more fish. Too many fish directly results in too much ammonia in the water, which can quickly lead to conditions that are toxic to fish and invertebrates; even worse, if these fish die, then they can create an ammonia spike due to decaying organic matter.

For freshwater fish, it is recommended to only have one inch (2.5 cm) of fish per gallon (3.8 L) of water. More than this can and will lead to too much waste as well as a depletion of dissolved oxygen as more fish means less oxygen and more carbon dioxide.

Poor Fish Tank Maintenance

Lastly, a high ammonia level in the fish tank can be the result of poor maintenance. In general, it is recommended to perform partial water changes every week or every other week in a typical fish tank to keep nutrients down. Vacuuming the substrate also helps remove stuck organic matter and keeps anoxic areas from building up in the gravel or sand, which could potentially lead to nutrients leaking out later.

As we’ll discuss later, a simple water change is the best way of reducing ammonia levels in the aquarium; however, it’s best to keep on top of the problem by performing regular tank maintenance instead of waiting for the problem to present itself!

What Are the Symptoms of Ammonia in a Fish Tank?

If you suspect ammonia in your fish tank, you must immediately test your water to confirm the problem. Here are the signs that there could be an issue:


Fish tanks have a particular smell, but so does ammonia. One of the quickest ways to see if ammonia is in your tank is by taking a quick smell.

If you’re unfamiliar with what ammonia smells like, it is often likened to the odor of cat urine. The odor is crisp and foul-smelling, close to that of vinegar but still more fragrant.

This smell will intensify with the level of ammonia present, but in general, ammonia is detectable by scent in relatively small amounts.

Fish Behavior

Besides the odor, fish behavior will be the telltale sign that ammonia is starting to affect livestock.

Ammonia poisoning can happen relatively quickly and can lead to a slow and painful death for fish, invertebrates, corals, and even plants.

The main signs you will want to look out for are lethargy, gasping for air, and redness around the gills.


High levels of ammonia can directly burn the internal and external anatomy of your fish.

The gills are usually affected the most and can start to overcompensate with mucus to try to relieve the burn. This ultimately leads to a lesser ability to absorb oxygen and a loss of appetite.

Swimming becomes painful and exhaustive, leaving your fish tired or maybe even motionless at the bottom of your tank.

Gasping for Air

Along with lethargy, you might find that your fish is struggling to breathe. This is due to the mucus that has been generated to help relieve the burns as well as damage to the gills and internal organs.

In a tank with high ammonia levels, it is common to see fish breathing heavily and gasping for air. They will usually alternate between resting on the substrate and breathing heavily and gasping for air towards the top of the fish tank where dissolved oxygen concentration is highest.

Redness Around Gills

It’s possible that your fish doesn’t display any of the aforementioned symptoms, but develops redness around its gills instead. This is due to the damage being done in and around the gills.

These red spots can also appear across the body as the ammonia continues to burn. Along with being excruciatingly painful, these sores can become infected and lead to an even bigger problem.

What Are the Best Ammonia Removers for Aquariums?

There are a few ways to lower ammonia levels in the fish tank, all of which can be pretty easily done.

If you haven’t yet traced the source of the problem, keep looking for the cause of the ammonia spike. Ammonia will continue to be introduced into the water if, for example, something has died in the tank or if the aquarium is overcrowded.

Water Changes

One of the easiest and most efficient ways of lowering ammonia levels is by performing partial water changes. Water changes immediately remove ammonia from the fish tank and introduce safe water that will help dilute the remaining ammonia in the system.

It’s important to space water changes out over a couple of days to make sure that any fish or invertebrates aren’t being more stressed than they already are.

Once you have tested your water quality and found that ammonia is the problem, it is best to perform a large water change of 40-50%. Allow the system to realign and test the parameters the next day.

If ammonia is still present, perform another partial water change of about 20-30%. Allow another day and test the water again. Perform partial water changes as needed until ammonia returns to 0 ppm.

Aquarium Supplement

Water changes are usually the easiest way to solve a high ammonia level, but biological and chemical supplements may sometimes be necessary and can be helpful to speed along a new tank.

Water Conditioners

One of the best products to have on hand at any given point is a water conditioner such as Seachem Prime that removes chlorine as well as detoxifies ammonia, nitrite, and other heavy metals.

While this won’t solve the cause of the problem, fish and other livestock should be affected less, and more time will be given to figure out the root cause.

Beneficial Bacteria

Many beneficial bacteria products that may be introduced into your aquarium to help keep nutrients at ideal ranges. However, these biological supplements will not immediately reduce ammonia levels.

Instead, good bacteria is added into the aquarium to help accelerate the nitrogen cycle and process ammonia over the next few days.

Replace Your Filter Media

ammonia on aquarium

Ammonia spikes are often caused by a colony collapse of nitrifying bacteria on your filter sponge.

Therefore, replacing it with one from a healthy, cycled aquarium should help to reboot the nitrogen cycle and reduce ammonia over the coming days.

How Long Does It Take To Lower Ammonia Levels in the Fish Tank?

The problem with having ammonia in your tank is that you need to remove it as soon as possible all while not stressing out your fish even more.

With prompt water changes and chemical intervention, ammonia can usually return to safe levels within a day or two. Low levels can be solved with a simple water change, while higher levels might need several water changes and chemical support.

Whether ammonia levels remain at safe levels, however, depends on whether you’ve solved the root cause of the problem, and prevented it from returning.

How Do You Prevent Ammonia in Your Aquarium?

Test Kits

If you don’t know what’s happening with the chemistry of your fish tank, then you don’t know what’s happening biologically.

Testing for ammonia, nitrites, and nitrates is recommended every month for established aquariums, and more frequently in young tanks. Doing so will help you to identify any issues early on, so you can work on solving them quickly.

Test Your Source Water

Occasionally, ammonia may be present in tap water. If you have an ammonia problem, it’s worth testing your tap water to be on the safe side.

Keeping Live Plants

Aquarium plants tend to favor nitrate (NO3) as their main essential nutrient, though they are also able to uptake ammonia (NH3), ammonium (NH4), and nitrite (NO2).

In my experience, well-maintained live plants are an excellent way to help keep your water in a healthy equilibrium – just be sure to remove dead leaves to prevent them from rotting and releasing ammonia into the water.


If your aquarium has suffered an ammonia spike, you need to work quickly to save your fish’s lives. Partial water changes and chemical supplements are good emergency fixes, but you must also solve the root cause of the problem to prevent it from happening again.

Avoiding overfeeding, regular tank cleaning and good filtration maintenance are all essential to keeping ammonia levels at zero.

Sharing is caring!

32 thoughts on “How to Lower Ammonia in a Fish Tank: Pro Advice”

  1. Hi
    I have a small 17l tank which I only bought five weeks ago.
    I got some harlequins a week later but they died after a few days (even though I followed all my pet shop’s instructions).
    So I left my water to cycle without fish (albeit with the heater off and no light as I was away).
    Got five danios last week and they seem to be doing fine.
    But my ammonia level is still high-ish at around 1.5mg.
    My live plant also doesn’t look that healthy anymore.
    I’ve done a water change (25%) and hopefully that will help and have been adding half a teaspoon of healthy bacteria liquid daily.
    My nitrite level is almost zero and nitrate level is intermediate.
    I was thinking of removing the plant and getting a healthy one (I suspect the lack of light did not do any good).
    Is it just a matter of waiting for it to cycle fully?
    Can you overdose on the bacteria drops?

    • It is hard to pinpoint your exact problem, but yes, any issues you’re having right now are probably due to the cycle. I would suggest getting even more plants and waiting to buy fish/invertebrates; don’t throw out the plant you have until it’s fully dead. Run the tank on a regular photoperiod for your plants and keep the heater on. Continue to test parameters and things should start to even out soon.
      You can’t overdose on bacteria drops, though they aren’t effective after a certain point.

  2. Hi, I an currently doing undergrad research on zebrafish, which requires overfeeding. My experimental tank has 15 fish and the ammonia level is at roughly 1.25. I did a water change but it bounced back up. I am doing a water change tonight as a did a 50% change yesterday to fix this. Should I get some API Ammonia lock or clear to help, or would the tetra cleaning bacteria be alright to add?

  3. I have a cycled tank
    No fish in it for about 3 months now
    Ammonia between 1-2
    Have some Anubis in there also
    I do 50% 2 times a week
    I can’t get rid of ammonia

    • Hey Anthony!
      Make sure that your test kit isn’t expired. Also, make sure that your source water doesn’t have ammonia in it either.

  4. Hello,
    I have a tank of Betta, golden barbs and Cory Dora’s. They are all getting along no issue. But my ammonia has been staying high since 1 week of them being in it. Now it’s been 7 weeks and it’s still on 5. I don’t know what to do. I’ve reduced the feeding, done weekly water changes. The fish are not lethargic or not got the red spots they are just swimming around without any issues so far.
    Please can you advise? My ph is fine and I use test strips for the ammonia.

    • Hi Nissi,

      Test strips are very inaccurate. If possible, get a liquid test kit as soon as possible. Your local fish store might even be able to test for you.
      For now, I would be doing daily 25% water changes. If the 5.0 ppm is true, then you’re at high risk of stalling the bacteria in your aquarium which will quickly cause a crash.

  5. Hi! I’ve had my 10gal tank for about 3 weeks now, after a week I added in 3 white cloud minnows and 2 ghost shrimp (all are doing fine), last week I added in 2 guppy’s (one neon blue and one dragon head). I noticed 2 days ago that my dragon head guppy was acting odd, he would lay at the bottom of the tank and wasn’t as active nor eating when I fed them. When I tested my water my ammonia was 2ppm, I did a 50% water change and the levels went down to 1ppm, I did another water change yesterday and this morning the levels were .5ppm. Both guppy’s seemed to be doing better, but over the last 3 hours my dragon head guppy has started to swim erratically, corkscrewing through the water, spinning, with jerky movements and then lying upside down at the bottom of the tank, and his gills seem to be moving very fast.
    The rest of my fish are acting normal, and my water levels are normal, with the exception of the ammonia being lower that .5ppm, maybe around .2ppm? I have him isolated in a different tank right now, but I’m not sure what to do for him.


    • Hi Caitlin,

      It seems like your tank wasn’t fully cycled; adding the fish caused more ammonia than your tank could handle.
      I am curious to know your other water parameters. Ammonia is dangerous, but nitrite and pH can also be killers. It’s also possible that the guppy just wasn’t healthy to start with.
      In the meantime, continue with daily water changes. You don’t want your ammonia going much higher than 0.5 ppm. Don’t add any more fish (which you should add another 3 minnows) and continue to monitor levels.

  6. Hello, we have one Betta who has been breathing heavy and laying ok it’s side. We tested the water and came at 7.5. We read that it may be ammonia on the water that’s causing all this. Also, we read to pour some tap water to decrease the ph and also baking soda? Any suggestions how we can fix this? Also, will we need to take the fish out of the tank in order to treat the water?

    • Hi Andrea,

      I’m getting to this message a few days late so I am sure you have lost your betta fish already.
      7.5 ppm ammonia is unliveable. So much so that beneficial bacteria are unable to complete their processes, stalling the tank entirely.

      I recommend taking several weeks to understand the nitrogen cycle. If you don’t start out with stability and patience from the start, you will never have success with fishkeeping.

  7. been running for a week or two now will only small water changes it’s a five gallon but may be a 4 gallon not sure of water perimeters as i don’t have the tool should i get one immediately ?

  8. hi my fish has ammonium poisoning and constantly has red stripes that are fading and coming back bright red im doing 20-15% water changes adding in prime,stability,stress coat,stress zyme, api ammo lock and nothing seems to work in worried that i will wake up and find my fish floating at the surface it’s been almost a week now and i don’t know what else to do

  9. Hi,
    My tank has been cycling for about a month and i can’t get rid of the ammonia it has been siting around 20ppm. i have tried water changes and i brought a plant but that is not working. i have been given lots of different opinion by different people at different pet shops and nothing is working how could i get rid of it.
    P.S. i have white allege in my tank and i have sterilized it with hot water and has grown back in a matter of days what could be the becuase of that and how can a get rid out if for good (it is always in the same spot)

    • Hey Charlotte!

      Don’t worry about the white algae for now. When I hear of constant ammonia in a new tank I immediately think of source water. Can you test your source water for ammonia?

  10. Hello I have a 37 gallon tank with 3 african cichlids. I checked my ammonia le els are very high. I did 50 percent water change and added api stress coat and stress zyme. (My fish were swimming upside down. And looking pale when I notice there was something wrong). What else should I do in this situation? Thank you in advance

    • Hey Yordana,

      Sounds like it’s too late for your fish if they’re swimming upside down. Continue to do 25-30% water changes over the next few days. You can also pick up some Seachem Prime or beneficial bacteria supplements to help keep levels down.

  11. Hi I have 55 gal with 2 canister filter cascade 1000 and a sun sun for 55 gal I have a bare bottom tank 2 wave maker and a fish waste filter that sucks the had the tank for about 5 months but can seem to get the tank to cycle I get ammonia spike every 3 days. I do a 40% change test the water everyday but every 3 days the ammonia goes up. I have 2 small Oscars and 1 pleco. Between the 2 canister filter I have almost 7 lbs of bio-media. I use Sea hem Prime to help the ammonia and use Seachem Stability as well. What I’m I doing wrong? Please help

    • Hey Lori!

      Yes, this is very difficult to understand! Once you understand that beneficial bacteria don’t live in the water column, it starts to make more sense.
      Instead, they live mainly in the media of your filter, but will also populate the substrate, decorations, etc. When you do a water change, you are not removing that bacteria because they are not present in the water. The main point of doing water changes is to control nitrate levels, which can’t be processed by the beneficial bacteria in the aquarium.
      Hopefully this makes more sense, but let me know if you need me to break it down even more.

  12. I have a 90 gal tank. I can’t get my ammonia out of my tank. I’ve done water changes, cleaned it, bought a fx4 filter, I’m beside myself. It’s been a week. Do I just need to let the tank cycle ? All my other levels are perfect…


    • Hi Kim!

      Sounds like you have a source of ammonia. Are you using items from another tank? Did you seed the tank with shrimp or fish food?

      If the tank is new, I would wait to see signs of a cycle.

    • Yes! Plants can actually take up ammonium, ammonia, nitrite, and nitrate. This is why a ‘clean’ tank with 0 ppm parameters across the board is not ideal. Your plants get nutrients from the water column and/or substrate, so they need to be fed via fish or fertilizers.

  13. Hi! I’m hoping you can help. I started a small beta tank. It’s only 2 1/2 gallons. I let the tank filter for a week before I added two female betas. 3 weeks in the water looked cloudy (here I found out I shouldn’t have done anything afterwards) I went to my local pet store they tested the water everything was perfect ammonia 0. She told me to change the water by 50% for the cloudiness. She also told me to rinse the filter of under tap which I read later is a no! Rinse in aquarium water! And then I found out the cloudiness is normal and it was cycling. Now I’ve been battling ammonia since I tested the water on Monday. I took a sample in. I did a 50% water change. Today I went and bought an API test kit. Still ammonia. I did a 20% water change. I also bought an extra filter machine and ammonia filters to add. How long until the tank reestablishes itself? I wish I never would’ve conducted that first cleaning as the water tested great but was just cloudy. Also I find many different answers for how much ammonia is except able. I’ve read only 0. Thank you for your help!



    • Hi Bonnie!
      The best thing you can do is NOT listen to pet store employees. There are some that are versed in what you’re actually supposed to do, but for the most part, they give bad information.
      2.5 gallons is way too small for two female bettas. The minimum size recommended for one betta is 5 gallons unless you’re willing to do more maintenance.
      In the future, yes, you need to cycle your tank for 3-6 weeks ahead of time. One week was not enough time and you are probably getting the cycle now.
      The best thing you can do at this point is to do daily water changes to keep ammonia and nitrite down because these can be lethal to fish.
      Yes, 0 ppm ammonia is the only level of ammonia you want to have. Anything above that can cause lasting damage. That being said, your fish should be able to endure some days of 0.25 ppm. But this is where the water changes come in to keep those levels down.
      I recommend watching many videos on the aquarium cycle and purchasing some bottled bacteria. Continue to test levels daily.

  14. You got my attention when you said that fish tanks are prone to algae and bacteria outbreaks due to high ammonia levels. My husband and I are interested in caring for fishes as we think that they can be a good stress reliever. Since we want to keep the fish tanks clean and free from ammonia that could poison fishes, we will consider using an acid neutralizer for a solution of ammonia in water.

    • Hi Shammy!
      Ammonia isn’t a direct cause for algae.
      Usually, algae is due to high nitrates and phosphates along with poor tank maintenance, too much light, or not enough water flow. However, traces of ammonia are MUCH more concerning than having algae in your tank at this point!!
      Any amount of ammonia in your tank can prove to be lethal for fish and invertebrates. You want to find the cause and fix it as soon as possible.
      Make sure you’re not overfeeding, your tank isn’t overstocked, and you’re doing regular water changes. The best way to get rid of ammonia is by doing large 25-30% water changes over the course of a few days. This should help get levels down without stressing your fish.
      A neutralizer will work temporarily but improving tank maintenance and finding the cause of ammonia is the only way for success in the long run.


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.