How to Save Dying Fish After a Water Change

The main part of aquarium maintenance is changing the water regularly, but if you’re not careful, it can shock your fish and cause them to die. Needless to say, no one wants a dead fish on their hands.

The good news is that carrying out a water change without screwing it up can be easily done by paying attention to a few things. For example, if you don’t want your fish to get all shaken up, carefully equalize the temperature of the water you are taking out with the one that goes in.

Read more to learn how to save dying fish after a water change.

Why are Water Changes Needed

Partial water exchange is a vital activity for a properly functioning system. Without carrying out this task, it is impossible to maintain an aquarium with healthy fish.

As much as the filtration system and plants can handle most of the pollutants, many more keep piling up in the water. In addition, some filtration metabolites (such as nitrate and nitrite) are mainly removed via water exchange.

Water also carries minerals absorbed and used by all aquarium inhabitants, plants, and animals. Partial replacement will keep levels within optimal range and prevent pH and hardness from dropping.

In a nutshell, partial water changes are all about removing excess organic matter and compounds dispersed in the water that can screw up your aquarium and make your fish sick.

How to Save Dying Fish After a Water Change

Want to learn how to save dying fish after a water change? It’s easier than you think. Here’s all you have to do.

1. Clean Out Leftover Fish

Like all other animals, fish and invertebrates naturally excrete substances and organic matter such as feces, respiratory residues, etc. In a simplified way, these residues are loose in the water. The aquarium bacteria will break down a part of it.

These bacteria will break down the ammonia into nitrite and nitrate. All these substances are toxic to different degrees. Nitrate is the last to be formed.

The interesting thing about nitrate is that there is no other way to remove it from the aquarium other than by direct absorption from plants (where plants will use only a part of the total nitrate concentration) or actively via partial water exchange.

Bacteria will break down residues of organic matter in the substrate. These bacteria will break down feces, food scraps, and leaves, generating ammonia and nitrate.

2. Remove the Buildup of Elements and Minerals

The decomposition of organic matter will still generate many other compounds, such as phosphates. All these compounds are toxic and are only removed from the system by changing the water.

We must think of aquarium water as the air we breathe. When we are in a sealed room, our breath releases CO², which is toxic to us. If there is no air renewal in this room, we will suffocate.

Another essential point, which few people realize, is that fish and plants extract minerals necessary for their development from the water. These minerals like Calcium, Magnesium and many others are suspended in the water, ready to be captured and used. They will even help the water maintain its pH and hardness.

As it is a closed system, domestic aquariums rarely have an automatic metering and dosing system for these compounds, so changing the water also replaces these minerals and avoids the fluctuation of the chemical parameters of the tank water.

What Can Go Wrong During a Water Change?

As simple as changing the water may seem, you should stay tuned and follow some basic rules so that everything ends well.

The main mistake of aquarists is to take a percentage of water from the aquarium and fill it with water directly from the tap. The difference in parameters will shock the fish; if this difference is too extreme, it will kill them almost immediately.

Another mistake is to disassemble the aquarium and wash everything under the faucet. This will kill the colony of bacteria we are trying to grow to act as our filter.

Using soap or other cleaning products is something commonly done by beginners. However, this should never be done, as residues will slowly poison the fish. Changing less water than necessary is also a mistake that can be fatal, raising the pH and making ammonia super toxic.

Top Reasons Fish Die after Water Changes

With everything mentioned so far, it is easy to understand why some people sometimes lose some fish after changing the water. But don’t worry; you need to understand the theory behind everything and adjust your handling. That way, you will fix the weak points and never lose other fish in this vital process for your tank.

1. Nitrate Levels are Too High

Before carrying out a water change, it is vital always to carry out tests in your aquarium. The minimum to be tested is the pH index with the nitrogen compounds (ammonia, nitrite, and nitrate). These indices will tell us how much water we need to renew.

The toxicity of ammonia changes considerably concerning pH, becoming more toxic the higher the alkalinity of the water.

People often follow incorrect information that it is only necessary to change 20% of the water monthly or that anything over 30% will kill everyone.

These statements are incorrect, and as long as you follow the information contained here, the greater the amount of water you change, the better it will be for the aquarium and its inhabitants.

Nitrogen compounds are highly water-soluble substances; that is to say, they are spread and concentrated throughout the aquarium water. In addition, these compounds are generated through organic matter; this organic matter, in excess, has the power to acidify the pH, leaving the ammonia less toxic.

In the case of an accumulation of ammonia, nitrate, or nitrite, the pH will remain low, reducing the toxicity of these compounds. In this case, when performing a partial water change below 50%, we increase the pH and still leave concentrated ammonia in the system.

If this happens, the fish will likely die from poisoning. That is why it is essential to carry out pH and nitrogen tests after the water change.

2. Suboptimal Water Change

The amount of water to be changed is often variable. The best thing is to be cautious and carry out weekly maintenance, with water changes ranging from 30 to 50% of the total volume. In these cases, we will know that the system will always remain stable, but if you delay the exchange for a week, you will have to exchange a larger amount.

Most people take the same amount of water, around 30%, monthly or fortnightly. So it happens that in 2 to 4 weeks, numerous biochemical reactions will occur in our aquarium, causing an increase in several compounds.

By removing less water than necessary, we maintain a high concentration of these toxins, which will gradually poison the fish.

The way to combat this is always performing as many tests as possible on the aquarium water before and after the water change.

3. Osmotic Shock

This shock occurs when we insert water with different parameters from the one we remove from the tank — causing an abrupt change in several physical-chemical indices. This sudden change causes a physiological shock to the animals.

The physiological shock occurs as fish adapt quickly to different pH, temperatures, and hardness. Many species are sensitive and will die of physiological exhaustion from shock.

4. Temperature Change is Too Drastic

When performing the water change, it is necessary to equalize the temperature of the water that will enter the tank with the one we have just removed. If this factor is not carried out, there is a high possibility that your fish will suffer some shock.

5. Lack of Water Conditioning

The water from the supply network contains some products that make it drinkable for mammals, such as chlorine and chloramine. However, these compounds are toxic to aquatic animals. Water can also be contaminated with heavy metals and other harmful substances.

To make the water usable in our tanks, we must always use a high-quality water conditioner. This conditioner will instantly remove all harmful substances from the water.

Be sure to use a high-performance conditioner. Inferior quality conditioners can release ammonia through the breakdown of chlorine.

6. Beneficial Bacteria Died

The death of beneficial bacteria is one of the worst things that can happen. This only happens when maintenance is performed very wrongly.

For the beneficial bacteria in your aquarium to die, the following must occur:

  • Extreme shock by temperature, hardness, or pH;
  • Chemical poisoning;
  • 80 to 100% water changed without using a water conditioner;
  • Allow the biological filter media to dry; and
  • Cleaning the entire aquarium directly with tap water.

You should never wash the aquarium; everything to be cleaned, such as the filter, media, and decorations, should be washed and rinsed with the water you removed from the aquarium. This prevents the death of bacteria.

How to Know If Fish is Dying After a Water Change

If you make a mistake during the water change, your fish will instantly show symptoms that something is wrong.

Fish Losing Color

The main symptom you will see is the fish losing color, and becoming pale and dull. However, it would help if you observed, as this also occurs when fish are not used to receiving maintenance in the aquarium.

If this occurs only because of the stress generated, the fish will lose their color but remain responsive and attentive. If it’s something worrisome like shock or poisoning, the fish will be panting and quiet.

The gills will turn dark red, and the fish may be on the surface or immobile at the bottom of the tank.

The symptoms have different causes, but the treatment is always the same.

Test the physical and chemical parameters of the water that came out of the tank and the water in the tank after the renovation. There will likely be a discrepancy in one of the factors, whether it’s high chlorine or a difference in temperature or pH. After you correct this difference, the system will be destabilized, and the fish will recover quickly.

Fish Staying at the Bottom of Tank after Water Change

This is a clear sign that something is wrong. Pisces are immobile at the bottom of the tank when they are trying to conserve energy after suffering a lot of stress. It is a troubling symptom, and you should take action quickly.

Fish Swimming Erratically after Water Change

Just like when the fish is close to the substrate, it is a symptom with multiple causes and must be treated quickly.

This symptom is more common in cases of chloramine poisoning.

How to Prevent Fish from Dying After a Water Change

This part is easy. First, as said before, equalize the incoming water parameters with the aquarium’s.

You should adjust the water parameters before putting new water in the tank. The best way to do this is with the help of a bucket and the necessary products.

We all know our aquarium’s basic parameters, which will always be constant. However, our faucet water can vary throughout the year, so it is vital always to test it before a water change. You should always have an aquarium water precision testing kit.

The best way to make adjustments is to fill one or more buckets with new water. Then, carry out the tests and, if necessary, make the adjustments with the help of products (like buffers) and heaters. After the adjustments, wait a few minutes and perform the tests again.

If everything is stabilized, proceed with the water renewal and slowly pass the water from the bucket to the aquarium.

That way, you have complete control over the chemistry and physics of the water, making it very difficult for temperature or pH shocks to occur. By testing the aquarium water, you will know the amount of ammonia, and if the pH is stable, then you can calculate the amount of water to be removed.

In partial changes, the amount of water to be changed can vary from 30 to 80% of the total volume, depending on several factors.

How to Perform a Proper Water Change

For the water change to be carried out correctly, it all starts with carrying out tests and removing the water from the tank.

After testing the aquarium water, remember to record the results. The next step is to test the water supply network and correct and stabilize its parameters for those already predetermined for your aquarium.

After correcting the parameters, use the water conditioner. From there, start the water exchange; for this, you should use a siphon.

The siphon is nothing more than a nozzle attached to a hose that, through gravity, will pull solids along with the water out of the aquarium.

Focus the siphon nozzle on where there is accumulated dirt between the substrate. Always remove the water with the dirt in the aquarium. Be careful not to suck in fish, plants, and other tank inhabitants.

After removing the desired water, fill the aquarium with new water. You can do this with the help of buckets or a pump.

Reconnect your equipment and check the test results of the renewed aquarium water. If necessary, make adjustments; otherwise, it is ready.

Top Tip: How To Completely Avoid Water Changes Death

Performing the proper water change is like a cake recipe; you can’t go wrong if you follow all the baking steps. The golden tip is never to use predetermined numbers that you find in some dark corner of the internet.

Get to know your aquarium and your fish, constantly test in the water and understand the variations your tank undergoes over time. Only then will you know the best frequency and quantity to be exchanged.

Another tip is always to continue performing routine procedures. The stricter the water change regime, the fewer adjustments you will have to make, and the less your fish will suffer.

Water change is essential in all aquariums; only through it can we eliminate unwanted compounds that are free in the water. Contrary to popular belief, this procedure is highly beneficial, especially when renewing a large part of the water in the tank.

To avoid losses and problems, you should always follow basic rules, the main one being equalizing the new water with the indexes of your tank.

Each aquarium has different times and cycles, so rules like 30% monthly water changes are only valid for some. Even if you have more than one tank in your house, you should know each system individually, as each one will have a unique need.

Final Words

So that’s how you save dying fish after a water change. Use the ideas expressed here to rethink your maintenance routine and how you change your water. Through simple steps, you can make this task more efficient and less stressful for your beloved fish.


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