How to Save Dying Fish After Water Change: 5 Simple Ways

Partial water change is essential for the proper functioning of an aquarium. But, your fish can quickly enter a dying state when done incorrectly. Therefore, learning how to save dying fish after water change is crucial. 

You can save dying fish after a water change by adding a stress coat water conditioner, increasing aeration, and adjusting the temperature. You can also add some aquarium salt to the water to help the fish recover and keep them in a fasting state to allow time for recovery.

In the rest of this article, I’ll dive into details on how to save dying fish after water change. I’ll discuss the symptoms to look for in fish to know how best to save them and how to conduct safe water changes to avoid this unfortunate event in the future. Keep reading! 

How to Save Dying Fish After Water Change: 5 Easy Ways

how to save dying fish after water change

There’s really not much you can do to save dying fish once you start observing the symptoms. 

However, you should begin by testing the water parameters, like temperature, PH, and oxygen levels, to determine the exact cause of this situation and know how to correct it. 

Simple things like forgetting to add a de-chlorinator or conducting the water change too quickly can tamper with the water parameters and stress the fish. 

On many occasions, chemical imbalances and temperature changes are the main reasons behind your fish’s dying state after a water change. 

Here are the different ways to save your dying fish after water change:

1. Improve Water Aeration

It’s essential to increase aeration in the aquarium if the water oxygen level is low. You should notice the fish exhibiting suffocation signs like:

  • Rapid gill movements
  • Labored breathing
  • Lethargic
  • Staying at the top of the water more than usual

The following are the main causes of oxygen deficiency after water change in an aquarium:

  • Elevated water temperatures
  • Chemical poisoning, such as chlorine
  • Stagnant water

But before we discuss how to improve aeration in water, it’s essential to know the difference between oxygenation and aeration. 

Oxygenation is the addition of oxygen, while aeration entails both oxygenation and water flow.

So, to improve aeration, you’ll need to increase the water oxygen levels and boost the flow rate.  

You can increase aeration in the aquarium by stirring the water manually.

Alternatively, you can also fill a small container with some aquarium water and slowly pour the water into the tank from a distance to increase water movement. 

You’ll need a reliable filtering system to guarantee optimal oxygenation and aeration for a more permanent solution. 

It’s advisable to combine the filter with an air pump or attach a spray bar to the outlet to increase oxygen content by distributing water around the tank. 

You may also add more plants or air stones to the tank. 

If you have a small tank, consider upgrading to one with a larger surface area to increase contact between the aquarium water and atmospheric air. 

Find Out: 8 Signs of a Dying Pleco and How to Save It

2. Add a Stress Coat Water Conditioner

Sometimes a water change can result in chemical poisoning, which is detrimental to the fish. This happens mostly when you use tap water from the municipal supplier in your aquarium. 

Tap water is usually treated with chlorine and chloramine to make it safe for human consumption. These chemicals are, however, toxic to fish.

A water conditioner will be handy if you use tap water to fill your tank or suspect your fish is dying from chemical poisoning. 

The conditioner neutralizes chlorine and chloramine immediately, making the water safe for fish. 

Some conditioners, such as Seachem Prime, can even eliminate excess ammonia and nitrites and detoxify heavy metals in water. 

So, a water conditioner should be a staple in your emergency aquarium kit. 

In fact, it’s recommended to add a conditioner to tap water in a bucket before filling up the tank. In other words, you should never fill your aquarium with water directly from the tap without dechlorinating it

You should follow the manufacturer’s instructions while using the conditioner because too much of it can also cause fish demise. Therefore, you should consult a professional if you’re uncertain. 

3. Adjust the Water Temperatures

Most fish thrive between 76 and 80℉ (24.44 and 26.67℃) temperature range. Some species need several degrees warmer, while others require temperatures a few degrees cooler.

That said, since fish are cold-blooded creatures, their body temperatures change with changes in water temperature. This means the environmental temperature has a direct impact on their metabolism. 

The fish will undergo stress if the water is extremely cold or warm. 

Low temperatures slow fish’s metabolism, making them sleepy and sluggish. On the other hand, high temperatures speeds up their metabolism, making them hyperactive. Moreover, warm waters have less oxygen, therefore, can cause fish suffocation.

It’s noteworthy that slight temperature changes can’t harm fish—if it happens gradually. However, the fish will undergo sudden thermal shock if the changes occur drastically. 

That said, you must set the aquarium heater to temperatures perfect for your fish species. A thermometer is vital for that.

Moreover, consider investing in good water heating equipment. One with a sensor that aids in automatic water temperature regulation.

Also Read: Koi Fish Swimming Upside Down: 4 Causes and Treatments

4. Replenish Aquarium Salt

If you’ve conducted all the water tests and ruled out all the chemical imbalances, the next action is to try aquarium salt. 

Aquarium salt is another must-have in your kit. It provides essential electrolytes for a fish’s health and vitality. 

Aquarium salt lowers stress, improves gill functioning, and speeds up the healing process, helping those suffering from water-change-related symptoms to recover.

It‘s also beneficial in treating fish infections caused by bacteria, fungi, and parasites.

You’ll want to replenish these electrolytes after every partial water change to help the fish manage the stress that comes with it

Finally, you should also use aquarium salt sparingly—too much of it can harm fish in the long run.

5. Stop Feeding the Fish

You need to understand two things. First, when a fish is dying due to a drastic temperature drop, its metabolism, including the digestive system, starts shutting down. Therefore, it may not digest food properly, resulting in bloating, constipation, and even compaction. 

Compaction is a severe case of constipation. It’s when the fecal matter gets stuck and dries out in the body when the intestines stop producing mucus—a life-threatening condition.

Therefore, you’ll prevent these complications and save your dying fish by not feeding it.

Secondly, a fish usually stops eating when under stress. So, any food put into the tank will sink and decay. This will raise ammonia levels, upsetting the environment further and causing more issues than there are already. 

On that note, make sure to remove uneaten food and keep the fish in a fasting mode for some hours to allow time for recovery. 

While you can apply these treatment methods when your fish exhibit symptoms of severe stress or shock, there are ways you can prevent such problems from happening in the first place. We’ll be discussing that in the next segment.

How to Prevent Fish Death After Water Change

Performing a water change in a fish tank

Prevention is better than cure for apparent reasons; you want to have your wet pet for as long as possible. Here are the different ways to prevent fish death after water change:

1. Adjust the Incoming Water Parameters

The first step to achieving a safe water change is matching the parameters of the incoming water to that of the tank. 

While our aquariums’ key parameters are almost always constant, those of tap water vary constantly. 

Therefore, testing any incoming water before a water change is essential. This is where an aquarium water testing kit comes in handy. If you don’t have one for whatever reason, consider getting the API Freshwater Master Test Kit. It is the most preferred choice among aquarists. 

You’ll start by filling a bucket or more with the new water, then conduct the necessary tests. Check the temperature and pH.

If necessary, modify the freshwater using buffers and heaters to match the aquarium’s conditions.

After making the adjustments, wait a few minutes and conduct the test again. Proceed with the replacement when the new water parameters match those of the aquarium. 

Pre-testing and adjusting the water chemistry will help prevent temperature or pH shocks.

2. Dechlorinate the Water

I have already mentioned that using tap water can seriously affect fish. This is because of the presence of chlorine and chloramines, which are toxic to fish. 

However, most people use tap water in aquariums, and that’s understandable. It is readily available, and you can quickly have as much as you need, making water changes achievable at minimum cost and effort. 

You’ll, however, need to dechlorinate tap water before using it. Here are the best ways to dechlorinate tap water for use in an aquarium:

  • Letting the water sit: Allowing your water to sit out in the open will dissipate the chlorine naturally. It is the cheapest method, but it takes time. It will take about 1-2 days, depending on the water quantity and the amount of sunlight and air. The more the sunlight and air, the faster the dechlorination process. 
  • Boiling the water: Boiling is another easy, effective, and safe method of removing chlorine without disrupting the water’s chemical composition. It also doesn’t cost as much, but you’ll need to boil a few pots depending on the size of your fish tank. You should boil the water for 15 to 20 minutes for effective dechlorination. 
  • Using a water conditioner: A water conditioner is a chemical that quickly and effectively eliminates chlorine and other substances in tap water. You’ll, however, want to ensure that the product you use doesn’t affect the water’s pH.

Of the three methods, I recommend using a water conditioner. The two other methods will only eliminate chlorine. But, using a water conditioner will help remove other toxic substances, such as ammonia, chloramines, and heavy metals. 

Alternatively, avoid tap water and use safer options such as distilled, de-ionized, and reverse-osmosis water. 

3. Perform a Proper Water Change

You can proceed with the water change after testing, adjusting, and de-chlorinating the new water.

It’s worth noting that conducting a large water change at once is catastrophic to your fish.

For instance, doing a 40 to 50% water change every 3 to 4 weeks instead of the recommended 10 to 15% water change weekly. Although you may save time by doing that, you’re putting your fish at risk in the following ways:

  • Long durations before a water change causes the nitrates to build up to dangerous levels. On the same note, a massive water change at once will lower the nitrate levels drastically, inducing osmotic shock that can kill the fish.
  • Substantial water changes dilutes the nutrients that give your fish a stable and healthy environment to thrive. It also destroys many beneficial bacteria, leaving too few to deal with ammonia and nitrites. This puts your fish at risk of ammonia poisoning. 

Therefore, you should perform small and frequent water changes.

Water Shock Fish Symptoms

By now, you probably know that aquarium fish are sensitive animals. Any drastic environmental change can send them whirling.

Fish can go into water shock due to two things:

  • A drastic change in water temperature
  • A drastic change in water PH

When there’s an abrupt increase in water temperature, many fish will swim to the surface to gasp for air. This is because warm water contains less oxygen. 

Some will swim around hysterically because high temperatures speeds up metabolism, hence the hyperactivity. This can eventually kill them.

On the other hand, a drastic drop in temperature will slow their bodily functions. They’ll become sluggish and sleepy, and after some time, they’ll stop swimming and lie at the bottom of the tank. Some can enter into a coma. This state will be shown by floating upside down or sideways. 

Fish in a pH-related shock can exhibit a wide range of symptoms, but mostly, you’ll observe them huddled in a corner or lying at the bottom with drooping dorsal fins. They’ll occasionally jerk and dash, then return to the immobile state. Fish in this state appears pale and lethargic.

Here’s a summary of the most common water shock fish symptoms:

Cause High TemperaturesLow TemperaturesPH Change
Symptoms – Erratic swimming -Gasping for breath -Darting around– Lethargy
-Lying at the bottom -Floating sideways and upside down
– Lethargy
-Lack of appetite -Disoriented swimming -Huddling in a corner
Water shock fish symptoms


Now that you know how to save dying fish after water change, here are summary points to take home:

  • Always test and adjust the new water parameters to equalize that of the aquarium before changing
  • Dechlorinate tap water or use chlorine-free water for your aquarium
  • It is better to carry out smaller and more frequent water changes
  • Always observe your fish’s behavior following a water change and act immediately if they exhibit signs of stress

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