Betta Died After Water Change: Reasons & Best Ways To Save Your Fish

Water change is a frequent practice that every betta keeper should know. It guarantees that your pets always have optimal conditions to thrive. 

Unfortunately, some people claim that their betta died after the water change. So what are the reasons? How can you perform this task correctly without harming your fish? This guide will reveal the answers. Let’s check! 

Betta Died After Water Change

Changing the water in your fish tank may alter the tank’s conditions. Your betta may not withstand the sudden shift and become severely stressed. Some may die too.  

Nitrate levels

Nitrate drop is harmful to fish and can potentially be fatal at high concentrations in tank water. But a rapid decrease in nitrate levels after a water change could cause your betta to experience osmotic shock.

The shock refers to a condition where your betta can’t control its ionic compound absorption. The fish will consequently begin to either collect or emit too much fluid.

How to fix it?

Keep tank water changes to 10% or less to prevent osmotic shock from hurting or killing your betta. If you want to add more water, you can change the water partially but wait about one hour between the changes. 

Betta fish


Your betta may become ill or even die after a water change if the new water doesn’t precisely match the tank’s temperature

A fish that experiences temperature shock won’t move much, will soon lose color and may pass away. The immune system will weaken over time.

Moreover, your pet might be more vulnerable to diseases that its systems can resist when being healthy. 

How to fix it?

It would be best to perform water changes with previously warmed water to prevent fish deaths caused by thermal shock. 

Water temperature is crucial for your pet


Your betta will suffer if you fill your fish tank with tap water without first employing a dechlorinator.

In most cases, chloramine and chlorine are present in tap water. Both can kill almost anything in your tank and are dangerous to fish.

Adding chlorinated water to your tank during a water change will eliminate many beneficial bacteria that maintain the system’s continuous nitrogen cycle. 

How to fix it?

Dechlorinate new water before adding it to your aquarium so you can avoid damaging the biofilter or killing your pet with chlorinated water.

It could take a good dechlorinator around five minutes to effectively neutralize the chloramine in a specific volume of water.

Also, be aware that the filter may not eliminate chlorine and chloramine if you use water that has been through a RO or DI treatment for your tank’s water changes.

Dechlorinate new water for betta

Filter media 

Both substrate and filter media are porous materials that make fantastic habitats for beneficial bacteria. However, while changing tank water, you may remove many of them. 

The lack of beneficial bacteria will also interrupt the nitrogen cycle in your aquarium. The ultimate consequence is a “tank crash.”

Contrary to popular belief, if you replace filter media when cleaning your tank, the ammonia and nitrite level may spike and potentially kill your fish. 

How to fix it?

When you clean your fish tank, always wash the filter media in your fish water and vacuum about 30% or lower of the substrate at once to avoid harming your fish.

Clean the filter media regularly

How To Change Water Correctly Without Killing Betta? 

To do a water change without running the danger of killing your betta, stick to these steps: 

  • Fill the tank with the appropriate amount of water.
  • Warm up the new water until it matches the current temperature of your fish tank. A small heater can help you easily heat up the water in your container. 
  • Dechlorinate water and wait for the dechlorinator to properly remove chloramine from the tank. 
  • Water changes in betta tanks should not exceed 10% every session. If you have to go beyond it, allow your pet enough time to adjust to the next water change. 


1. How do you save a dying fish after a water change?

To save your dying fish, perform these steps:

  • Detach the filter
  • Check the water condition and treat it with salt or heat 
  • Look for symptoms in other fish of the same tank
  • Give your fish veggies or low-protein food

2. Can you do too many water changes?

No. One water change a day is the maximum frequency, according to experts. 

If you want to perform the changes every day, only replace 50% of the tank water not to disturb your aquarium’s biological balance.  

3. Is 50% water change too much?

No. But you should never go beyond 50%. There is a chance that you’ll kill the beneficial microorganisms in your aquarium. 

Moreover, your fish can’t withstand sudden fluctuations in their living conditions, which result from over 50% water change. 

4. What is new tank syndrome?

New tank syndrome describes issues of invisible, poisonous substances gathering in a tank. It gets the name because you often see it when setting up a new aquarium, and your filter is growing. 

5. How do you help a stressed betta fish?

It depends on what problem your pet is facing. But in general, your betta would love it if you:

  • Check the water parameters
  • Use water conditioner drops
  • Add more hiding places
  • Use tannins 

You can learn more tips to take care of your betta right here: 


Your betta may die after a water change for some reasons, such as nitrate level, water temperature, chloramine or chlorine, and filter media. 

There are many things to learn about water changes. Also, pay attention to any signs of diseases so you can save your pet. 

Hopefully, you will find this article helpful. For any further information, please feel free to ask. Thank you for reading!