Ammonia Still High After A Water Change: All Reasons & Solutions

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I’ve noticed numerous times that my tank’s ammonia levels remain high after a partial water change. Sometimes, the concentration even spiked and got higher than what it was in the beginning.

As the years passed, I gained a lot of experience with the issue and learned how to fix it. Now, I am willing to share my knowledge to solve the situation in your tank.

Ammonia tends to remain high after a partial water change due to deep cleanings, in which ammonia-reducing bacteria is removed from the tank. However, ammonia also spikes after water changes due to inadequate cycling and malfunctioning filters.

As we proceed in this article, I will share a few other reasons that may elevate your ammonia after water changes. I will also present a few essential steps you can take to solve the issue and prevent it from recurring in the future. 

Why Did I Get An Ammonia Spike After A Water Change?

Every aquarist understands the importance of controlling the ammonia concentration in their tank. The substance causes distress, disease, and death in fish.[1]

That is why you are encouraged to keep the ammonia levels in your tank at zero.[2] Most aquarists are also aware that water changes can reduce or even eliminate ammonia in an aquarium.

However, some of you have tested for ammonia after performing a water change only to find that the ammonia levels were still dangerously high.

Is that normal? No, it is not. But it happens all the time, and it has been linked to various factors and causes, including:

1. Insufficient Cycling

The purpose of cycling your tank is to introduce bacteria that can turn ammonia into nitrites and nitrites into nitrates.[3]

You cycle a tank by adding ammonia to it. You can do this by introducing one or two fish.

The waste they excrete will produce the ammonia your tank needs to establish a colony of the Nitrosomonas and Nitrobacter bacteria that convert ammonia into nitrites, and nitrites into nitrates.

Proper cycling can take anywhere between two and seven weeks. However, it is relatively commonplace for fish owners to introduce fish to tanks that haven’t been wholly cycled.

In other words, the tank doesn’t have enough good bacteria to contend with all the ammonia the fish are adding to the water via digestion and excretion.

In such situations, aquarists will find that water changes are incapable of keeping ammonia concentration down.

By the time they test their water after a water change, the ammonia levels have already risen because the bacteria that would typically combat the substance is absent.

Solution: Introduce beneficial bacteria that convert ammonia into nitrates:

  • Add bacteria starter culture with products like the API QUICK START (link to Amazon).
  • Add filter media or substrate from a well-established tank.
  • Let your tank sit for a couple of more weeks until the bacteria form naturally.

2. Water Conditioners

Some people use chemicals to remove toxins from their tanks without taking the time to understand how those products work.

For instance, water conditioners like Seachem prime and Amquel do not remove ammonia. They merely neutralize its toxicity, converting it into a harmless form.

It is still ammonia, but it isn’t dangerous to fish. That gives the good bacteria in your tank an opportunity to convert it into nitrites and nitrates.

However, the average test kit cannot differentiate between harmful and harmless ammonia.

As such, if you test for ammonia shortly after using water conditioners, don’t be too shocked if the ammonia levels are seemingly unchanged.

How does this relate to water changes?

Well, water conditioners do not stop at turning ammonia into harmless ammonium. You can also use them to eliminate chlorine and chloramine, mainly if your water came from a tap.

That is a problem because many water conditioners remove chlorine and chloramine by turning them into ammonia.[4]

Suppose you just performed a water change to remove ammonia. In that case, an effort to eliminate the chlorine and chloramines from the tank using specific water conditioners will only succeed in introducing more ammonia.

Fortunately, those same water conditioners will make that ammonia harmless.

But, as was mentioned above, your test kit won’t differentiate between harmful and harmless ammonia. It will merely inform you that, despite your water change, you still have ammonia.

Solution: If you use a water conditioner, read its description. If it removes chlorine and chloramine, don’t worry too much about the ammonia.

3. Deep Cleaning

Generally, you are encouraged to keep your aquarium clean. That usually includes vacuuming the substrate and removing debris.

However, there is such a thing as cleaning a tank a little too thoroughly. The bacteria that remove ammonia are found in the substrate and filter media. 

Therefore, if you clean the filter media and the substrate a little too efficiently, you could remove this bacteria, allowing the ammonia in the tank to run rampant.

That can also happen when you replace all your filter material at once.

Solution: Limit the way you clean your aquarium, with the filter media and substrate in particular.

4. Chlorine/Chloramine

Some people understand the importance of allowing the bacteria in their filter to thrive. They know that they shouldn’t replace their filter material unless it is absolutely necessary.

However, during a water change, they make the mistake of washing or rinsing the filter with tap water. 

If your tap water has a high chlorine and chloramine concentration, it may kill the filter’s bacteria colony.

In other words, you will return the filter to its place without realizing that it no longer holds the bacteria needed to combat ammonia.[5]

And because you still have fish in the tank continuing to produce ammonia, the ammonia concentration is just as likely to spike in the period after the water change but just before you carry out the test.

Also, if you’re using tap water for your water change, you should consider the possibility that the tap water has ammonia (bonded to chlorine).[6]

Solution: Dealing with chlorine and chloramine in tap water:

  • Let the water sit for 24 hours before being added to your fish (for chlorine evaporation).
  • Never wash the filter media with tap water.
  • Test the water you add with a testing kit to make sure it is free of toxins.

5. Overstocking & Overfeeding

Suppose your tank has too many fish, to begin with, and you made the mistake of overfeeding them immediately after a significant water change.

In that case, your tank will accumulate ammonia faster than the bacteria can convert it.

That is because massive water changes, which are supposed to eliminate ammonia, also remove some beneficial bacteria.

The same goes for any cleaning process that involves the removal of all the gravel at the bottom.

The bacteria you leave behind are incapable of accommodating so many fish producing so much waste at the same time in a small, crowded tank.

Solution: Use the one-inch-per-gallon rule, which says that for every inch of mature fish, you’ll need at least one gallon of water. For example, a goldfish that is 2.5 inches long will require 2.5 gallons, two goldfish that size will require 5 gallons, and so on.

6. Malfunctioning Filter

Have you checked your filter? Some people think that water changes are all they need to control their ammonia levels.

But if your filter has significant sources of ammonia, those contaminants will pollute your tank all over again.

That typically happens in filters that don’t work correctly and accumulate waste and toxins inside.

Even if the device contains bacteria that fight ammonia and turn it into nitrates, the rotten food, and debris will overcome it.

Solution: Replace your filter if you notice the following signs:

How Do I Fix High Ammonia Levels In My Fish Tank?

If you can’t find the cause of high ammonia levels after a water change, your next best option is to stop the ammonia from building up and look for the cause afterward.

Fixing high ammonia levels in your fish tank involves the following steps:

  1. Use active ammonia stabilizers such as Seachem and Ammo-Lock.
  2. Perform 50 percent water changes.
  3. Rise your filter using aquarium water instead of tap water.
  4. Remove rotten plants and debris from the top of the substrate.
  5. Avoid overfeeding your fish after water changes.
  6. Keep the pH above 7.0 to prevent ammonia toxification.

You cannot stop fighting the ammonia in your aquarium simply because the concentration has refused to fall.

There are additional steps that you can take to improve your tank’s ability to control the ammonia levels, including:

1. Commercial Products

Products like Seachem Stabilizer (link to Amazon) and Ammo-Lock (link to Amazon) will save your fish in an emergency by neutralizing the toxicity of ammonia.

That will give the good bacteria in the tank more time to turn the ammonia into nitrates, which are not as dangerous.

Let’s say that water conditioners have failed to deliver the results you want.

In that case, I highly suggest experimenting with filter media that is specifically designed to remove ammonia, such as API AMMO-CHIPS (link to Amazon).[7]

2. Proper Water Changes And Filters

It would help if you didn’t stop performing regular water changes simply because you keep recording high ammonia concentrations.

While you work to identify the ammonia source, continue to perform water changes (at least 50 percent). That is the only way to keep your tank clean, if only for a while.

As you have realized, a healthy tank requires beneficial bacteria that will turn ammonia into nitrites and nitrites into relatively harmless nitrates.

That is why you are encouraged to protect the bacteria colonies in your tank by applying caution whenever you perform regular maintenance.

For instance, you are still expected to clean the filters and substrate where the bacteria live. However, it would help if you only vacuumed the debris on the surface of the substrate.

If you are determined to take a more thorough approach, focus your efforts on only a third of the substrate in a week. 

This way, your maintenance efforts are less likely to eliminate all the bacteria in the substrate.

Where the filter is concerned, you can still replace the media. However, I suggest doing this a few pieces at a time.

Don’t replace all your filter media at the same time. Most importantly, when it comes to rinsing the filter media, use aquarium water, not tap water.

If you have determined that you don’t have enough bacteria in the tank, acquire some cycled filters from other aquarists. By adding them to your tank, you will grow your population of ammonia-eating bacteria.

3. Removing Contaminants

Remove contaminants that contribute to ammonia concentration in the tank, such as uneaten food, plants that are either rotting or dead, dead fish, and fish waste.

Don’t assume that your filter will eliminate all those elements. If you can see them in the water, take proactive steps to remove them.

Don’t forget to unclog the filter. However, as was mentioned earlier, you shouldn’t clean the substrate too deep or use tap water to clean your filter.

Instead, remove debris and rotten plants that stand out and sit at the surface of the substrate.

4. Overfeeding, Overcrowding, And pH

It would be best to avoid overfeeding your fish. Feed them once or twice a day, and give them the amounts they finish in five minutes or less. It is also just as important to avoid overstocking. 

Ammonia levels rise too quickly for aquarists to control in overcrowded tanks. Keep the right number of fish in a tank of the right size. That is especially true for relatively small tanks that don’t contain enough water.

It would also help if you thought about lowering the pH using chemical pH adjusters.[8] A pH above seven concentrates toxic ammonia.[9]

Lowering the pH is a temporary solution that reduces the risk posed by ammonia. It can protect your fish for a while until you perform a water change. 

I would also recommend increasing aeration by adding air stones and pumps. That will diffuse some of the ammonia gas (the toxic part) out of the water.

I personally use the Hygger Aquarium Air Stone Kit (link to Amazon). I like that particular bundle since its relatively heavy base prevents the fish from moving the device.

Above all else, you should only introduce fish to your tank after it has finished cycling. Bringing fish into an environment that isn’t fully cycled exposes them to unnecessary risks.

How Long Does it Take for Ammonia Levels to Drop?

If you have a new tank in the process of cycling, ammonia levels will start to drop after one to two weeks. However, if you added water conditioners, it will take a day or two for your testing kit to record a drop in ammonia levels.

Bear in mind that gradual changes are preferable when it comes to fish. Even though high ammonia levels could be toxic, letting it climb down at its pace would be the best choice.

However, if your fish look distressed and gasp for air, active products that stabilize the tank are the way to go.


If you’ve noticed a spike in ammonia after a partial water change, that is most likely due to deep cleaning. In that case, you’ve accidentally removed bacteria that typically reduce ammonia levels in the tank.

To avoid that, I highly recommend cleaning merely the upper layer of your substrate. You should also avoid rinsing your filter with tap water.

That could wash out the useful bacteria mentioned above. Also, tap water may contain ammonia that is bound to chlorine.

If you’ve noticed stress symptoms in your fish, such as sluggish swimming or air-gasping, you may use products that actively reduce ammonia. Those usually include necessary bacteria that stabilize the conditions in your tank.