Water Changes Not Lowering Ammonia? How To Fix Quickly

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If your water changes are not lowering ammonia levels in your aquarium, don’t panic.

There are lots of reasons why ammonia might not come down right away. These range from the removal of beneficial bacteria during water changes to the amount of ammonia in your tap water.

This article explains why you might not see ammonia reducing as quickly as you’d like after a water change, and what to do next to make your tank safe again for your fish.

What causes ammonia in fish tanks?

Most people believe that ammonia comes from excreted fish waste. This is true, but the majority is actually expelled through the gills. It is also released as uneaten food and other organic matter like dead plant leaves decompose in the tank.

You can manage ammonia levels in your aquarium by performing regular water changes. Also, clear out uneaten food and other debris before it has a chance to release ammonia into the water.

Why are my ammonia levels not dropping?

If the ammonia levels in your aquarium aren’t dropping after a water change, it’s usually because you haven’t changed enough of the water in your tank. Or you haven’t allowed enough time for the process to take effect. There are other potential reasons, but these are the main ones.

Here’s a breakdown of all the potential reasons you can’t lower ammonia in your fish tank:

Not enough water changes

It can take a while for ammonia levels to come down, especially if they spiked particularly high.

Even a 50% water change is only going to remove 50% of the ammonia. If you’re experiencing a large ammonia spike in your tank, it will take a few water changes to solve the issue.

Remember that when you do a large water change, you’re also removing beneficial bacteria that turn ammonia into nitrites. This means that large water changes can slow down the nitrifying process.

This is why performing smaller water changes more often is more effective than fewer, bigger water changes.

Change 10-20% of your tank water daily, using a water conditioner like Seachem Prime to dechlorinate your tap water. Monitor the ammonia, nitrite, and nitrate levels as you go to make sure your water parameters stabilize.

A word of caution: it takes 24 hours for the newly added water conditioner mix to fully cycle around the aquarium and mix with the existing tank water. Doing more than one water change per day is pointless as it interrupts this process.

Too little water changed

On the flip side, if you’re changing 5-10% of your tank water, you’re only removing 5-10% of the ammonia in your tank.

Changes this small simply can’t lower ammonia in a fish tank. Ammonia will be added to your tank quicker than you’re removing it.

Again, aim for a 10-20% water change every day until your ammonia levels are back to near-zero, and record your levels of ammonia, nitrite, and nitrate daily.

This will allow you to track changes in your parameters and react based on those movements. If your ammonia isn’t dropping after a few days, slowly increase the amount of water changed each time until you see results.

Your tank isn’t cycled

It’s perfectly natural if you’re struggling to lower the ammonia levels in a brand new tank.

The chances are you just don’t yet have the beneficial bacteria in your tank that turns ammonia into nitrites. This is only an issue if you’re doing a fish-in cycle.

When fish are added to a tank that hasn’t completed the nitrogen cycle, their waste releases ammonia. A non-cycled aquarium doesn’t yet have the capability to break down fish waste and it’s easy for ammonia to reach toxic levels.

This is why I’m not a big fan of fish-in cycling. While some highly experienced fishkeepers can use this method without losing fish, it means keeping them in conditions that are less than optimal for their health. It’s an unnecessary risk and causes suffering to the fish.

You’re already at a ‘safe’ level of ammonia

As long as your ammonia levels are low enough, you don’t necessarily need to eliminate them completely.

Depending on how your fish are behaving, a lot of hobbyists believe that levels of 0-0.25ppm are ‘tolerable’. Factors like pH levels and water temperature affect how dangerous a reading of 0.25ppm actually is.

If you’re struggling to reduce ammonia below 0.25ppm, look for behavior that indicates your fish aren’t comfortable. This includes:

  • Loss of interest in food
  • Red gills
  • Unusual or frantic swimming
  • Sluggish behavior
  • Trying to jump out of the tank
  • Swimming up and down the side of the tank (known as glass surfing)
  • Gasping for air at the surface of the water

If your fish seem fine, then either they’re not bothered by the low levels, or your test is showing a false positive. Many people run healthy community aquariums and never reach 0ppm on their ammonia tests.

You should always aim for 0 though as this is the only truly safe level of ammonia. When it comes to your fish and their tank mates, surviving isn’t the same as thriving.

How many water changes does it take to get rid of ammonia?

The number of water changes needed to completely get rid of ammonia in your tank will depend on a few factors. The biggest factor is how much ammonia is in the tank to start. Then it depends on how much water you replace with each water change.

For example, if your ammonia has spiked to 4ppm and you change 50% of the water, you can expect levels of 2ppm after a single water change.

What if the ammonia readings aren’t reducing in line with water changes?

The very simple math above assumes there is no ammonia in your tap water. Ammonia is often found in tap water as it boosts the effects of chlorine. When the two combine, they form chloramine, which is toxic to fish.

This is the reason we use dechlorinators like Seachem Prime, which make tap water safe for your aquarium. These products work by removing chlorine from the water and binding with ammonia to form ammonium.

Ammonium is a safer form of ammonia and can be consumed by the biological filtration system in your tank (read about this on Seachem’s website here)

Because these small amounts of ‘safe’ ammonia are now present in your water, it can look like the water changes aren’t as effective in reducing the problem. Water changes not lowering ammonia isn’t something to worry about, in this case.

This is why it’s important to compare the reducing levels of ammonia with the behavior of your fish. Ideally, each water change should gradually bring down the ammonia levels. Your fish should then start to look happier and behave more normally.

Many fishkeepers assume water changes aren’t working when actually, they’re seeing a false positive ammonia reading and the levels of toxic ammonia are gradually coming down.

Is it normal for ammonia to spike after a water change?

If ammonia levels appear to spike after a water change, this is probably because of ammonia being added to your tap water. If you’re using a water conditioner you should be fine, as these products convert ammonia into ammonium which is safe for fish.

Most of the time, if ammonia is increasing after a water change it’s because owners are not using a water conditioner. This means the ammonia in tap water is adding to the levels in the tank – the opposite of what a water change is meant to do.

If you are using a water conditioner in your water changes and ammonia levels are still showing as higher after water changes, don’t panic. It’s probably just the safe ammonium being detected by your test kit and your fish’s behavior should be a good enough indication of water quality.

Ammonium is still detected by many testing kits, so you’re probably seeing a false positive. However, if your fish are still showing concerning behavior, your filter may be to blame.

Don’t deep clean your filter!

Some aquarium owners make the mistake of performing a deep clean of their filter during a water change.

All you need to do is squeeze out the sponges and rinse the filter in the bucket of water you’ve removed from the tank. This will clean the filter media of excess dirt.

However, because the water is from the tank, it contains the beneficial bacteria needed to keep your nitrogen cycle alive.

If you’re deep cleaning your filter, you’re removing this beneficial bacteria. Ammonia levels are then left unchecked and your readings can spike.

Be careful not to over-clean your filter or the substrate where this beneficial bacteria is also found.

Malfunctioning filters

Over time, filters will need replacement or they’ll stop working and your nitrogen cycle will crash. This can be devastating to your fish and their tank mates, who rely on good water filtration to keep them alive.

If your filter media is clearly old and in need of replacement, don’t change it all at once. Replace one element at once to allow your sponges, carbon filters, etc. to accumulate beneficial bacteria before changing the next part.

Always keep a spare filter kit and expect to change your mechanical (sponges) and biological filter media roughly every 6 months. Chemical filtration (activated carbon) needs to be changed every 1-2 months. If you’re not sure what these terms mean, watch this video!

How long does it take for ammonia levels to drop?

How long it will take for ammonia levels to drop to zero depends where you’re starting from. If you’re cycling a new tank it will be around 6 weeks, but if you’re treating an ammonia spike in an established aquarium it could be just 1-2 weeks.

If you have a more severe ammonia spike, it may take longer and you’ll need to be patient and consistent with your water changes.

Because ammonia spikes can occur for different reasons, it can be hard to put an exact time frame on how long it will take to reduce. The key is to keep monitoring water parameters and doing 10-20% water changes every 1-2 days.

If ammonia levels haven’t dropped at all after the first week, gradually increase the amount of water you change. Don’t go too drastic or you’ll risk removing a lot of good bacteria. The idea is to change a little at a time and let your filter system do the work in between water changes.

How do you lower ammonia levels in a fish tank quickly?

As well as daily water changes, there are ways to speed up the process of lowering ammonia. These include installing air stones, lowering the pH of your tank, and using ammonia remover chemicals. However, sudden changes in water conditions can be bad for your fish.

An air stone will have more of a benefit in the long term, as it helps with gas exchange by disturbing the surface of the water. Ammonia is allowed to diffuse into the air and oxygen enters the water, making it much more hospitable for your fish.

Lowering the pH to a more acidic level is likely to be a temporary solution and won’t actually reduce ammonia. However, when you have a very high ammonia level it can help make life more bearable for your fish.

Ammonia becomes more toxic in more alkaline water. That means if you can lower the pH while you’re going through the process of lowering ammonia, your fish will have a better chance of survival.

Finally, there are ammonia remover products that you can buy that will help. However, I would only recommend this when you’ve had a very high spike in ammonia.

Some fish are very sensitive to changes in water conditions, so using ammonia remover may actually do more harm than good. The safest way is not to let ammonia spike in the first place, although this is easier said than done!

What is the best ammonia remover for aquariums?

If you’re experiencing a high level of ammonia and you’re worried for your fish, it may be worth considering drastic action. 

In this case, I’d recommend using API Ammo Lock. You can dose your aquarium every two days until ammonia levels reduce to a less worrying level, then continue with water changes as normal.


Ammonia spikes can cause serious harm to your fish, from general bad health to severe ammonia burns and even death.

Prevention is the best cure, so clear away any uneaten food and organic debris from the tank floor regularly. Always stay on top of your water changes, and monitor your ammonia levels weekly.

If you do detect an ammonia spike, the best way to bring the ammonia back down is to change 10-20% of the tank water daily.

If you don’t see the ammonia levels reducing right away, increase the amount of water being changed and consider installing an air stone to help diffuse ammonia at the surface.

In extreme cases, you can consider using a chemical solution like ammonia remover and temporarily lowering the pH to render the ammonia less toxic.

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