Why Did My Glofish Died After Water Change?

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Water changes are necessary for any fish tank since they prevent ammonia buildup, oxygenate the water, and cleanses the water of food particles and dirt.

How frequent you need to perform them and how much water to change every time differs based on a variety of factors.

These include the fish species you have, the tank’s setup, the fish’s age, how much waste they produce, etc.

Here are some facts to remember about water changes:

  • For most species, you should perform one water change per week and only change up to 15% of the water
  • Changing too much water at once will dilute the essential minerals and affect the tank’s beneficial biofilm, which, in turn, will affect your fish
  • Changing the water too often will produce the same effects and, plus, will stress out the fish
  • Fish fry require more frequent water changes (2-3 times per week) since they are more sensitive to ammonia and nitrite buildup
  • Inadequate water changes may cause your fish to die

Today, we will discuss the latter. Your Glofish have died after performing a regular water change, but why?

Here are the 5 potential reasons to consider:

Chlorine Poisoning

This is a common problem among novice fish keepers who haven’t researched the subject too much.

All of your problems begin with using chlorinated tap water. Water authorities add chlorine to tap water to kill off harmful pathogens and chemicals that may affect humans.

Chlorine is harmless for us, but it’s deadly to fish in high-enough concentrations. You don’t need much to create problems for your fish since regular tap water will do the job just fine.

How much chlorine will affect your fish depends on the fish’s age, size, and the amount of chlorine present in the water.

As a general rule, tap water may contain chlorine at levels between 0.5 and 2 ppm. These values will affect fish differently, as younger and smaller fish are more sensitive overall.

Depending on the severity of chlorine poisoning, your fish may get sick and die between several hours to several minutes following their contact with the substance.

The symptoms are similar to ammonia and copper poisoning or even low water oxygenation. The fish may appear to gasp for air, become lethargic, stop eating and swim erratically.

They will also display hyperemia, which are red patches on their bodies of different color intensities.

The solution:

Always de-chlorinate the water before using it.

There are 3 primary methods of doing that:

  • Aerate the water – You simply place the tap water into an open container with a larger surface area. It takes at least 24 hours for the chlorine to dissipate, but it may take longer, depending on how much water the container holds. To be sure, allow 48 hours for the aeration process to complete.
  • Boil it – Boiling the water won’t change the water’s chemistry or destroy oxygen as misconceptions go. But it will accelerate the dichlorination process dramatically. Just remember to cool the water before using it.
  • Use a reliable and safe de-chlorinator – There are several de-chlorinating products available that typically contain sodium thiosulfate. A water conditioner is ideal in this sense, eliminating harmful water chemicals and heavy metals, mineralizing the water, and combating fish stress via its vitamin B content.

Whichever method you prefer, always use a chlorine tester kit to make sure that chlorine has been neutralized and the water is safe to use.

Ammonia and Nitrite Poisoning

Ammonia and nitrites are deadly to your fish in high-enough concentrations.

The problem is that the rate at which ammonia levels increase varies wildly depending on a variety of factors.

These include:

  • How many fish do you have
  • The tank’s size
  • The fish’s size
  • Whether you overfeed your fish
  • How often do you clean the tank
  • If the tank has plants or not
  • If you have a filter or not

All these factors will drastically influence how fast ammonia buildup will occur.

As a general rule, overcrowding and overfeeding, combined with poor tank maintenance, make up for the most popular cause of ammonia poisoning.

The interesting aspect is that if your tank displays high levels of ammonia, changing 10% of the water will do no good.

Your fish will soon display signs of ammonia poisoning, including gasping for air, lethargy, erratic swimming, red or bloody gills, and lack of appetite.

Some fish are more sensitive to ammonia buildup than others, especially fry.

The solution:

There are several things you can do to prevent ammonia poisoning, such as:

  • Prevent overcrowding – Always provide your fish with optimal space. Overcrowding them will lead to more fish waste and more food particles decaying in the water and altering the water’s chemistry. This will create the ideal conditions for ammonia spikes, especially when combined with lacking tank maintenance.
  • Prevent overfeedingOverfeeding has a similar effect since uneaten food will sink into the substrate and rot. Decaying food is one of the primary causes of ammonia buildups.
  • Keep tank plants – Plants serve vital roles in any ecosystem, including the aquatic one. They will provide fish with hiding, oxygenate the water, dilute ammonia, and make the environment resemble more of a natural setting.
  • Consider bottom-feedersBottom-feeding fish species are useful in any aquarium since they consume food leftovers, diminishing the impact of occasional overfeeding.
  • Substrate vacuuming – It’s a must in most aquariums since it allows you to cleanse fish waste, food residues, and dead organic matter that may boost ammonia levels to unsafe parameters.

As a plus, always monitor ammonia levels in the tank water to know when the situation becomes dangerous.

Temperature Shock

This is another common issue related to unsafe water changes.

Changing the tank’s water is a great opportunity to mess everything up, especially when not paying attention to the temperature shifts during the process.

It’s common for novice fish keepers to skip the process of balancing the water’s temperature during the water change, which can lead to temperature shock.

Many species of Glofish are sensitive to sudden temperature changes, which stays true for all tank fish in general.

The problem comes when not monitoring the water’s temperature before adding it into the tank. This can lead to health issues or straight-up trigger temperature shock if the temperature is vastly different than that in the main tank.

The symptoms of temperature shock include rapid breathing, erratic swimming, gasping for air at the water’s surface, lethargy, coma, and even sudden death.

The solution:

Always monitor the tank water temperature and make sure the water you will add to the tank shows similar values. This will minimize the likelihood of temperature shock and make for a safer and more comfortable water change.

Huge Change in Water Chemistry

This is generally the reason why massive water changes are not recommended.

Changing too much of the water will dilute the minerals present in the fish’s habitat and disrupt the microbial balance, killing off the beneficial bacteria.

All parameters will be thrown off the charts, including pH, temperature, mineral content, water hardness, etc.

These sudden changes will affect your Glofish almost immediately, sometimes causing fast death.

The recommended rule is to never change more than 10% to 15% of the water every week.

Depending on your tank’s setup, the fish species present in the tank, and how many fish you have, you may not even need to perform too frequent water changes.

A 15% change every 2 weeks works just fine in many cases.

On the flip side, you also have fish species that require more water changes than others.

Mbuna cichlids are a good example, as these fish require weekly changes of 20% or more. But these are the exceptions, and you shouldn’t make decisions based on the exceptions.

The solution:

Never change more than 15% of the total water volume, and try not to perform water changes more often than once a month.

This is general advice that you should personalize to your unique case. Monitor the water parameters, check ammonia levels, and inspect your tank regularly.

Doing so will tell you how often you need to change your fish’s water and how much each time.

Filter Cleaning

Cleaning the filter is a necessity occasionally. The problem is that many people do it too often and too thoroughly.

You shouldn’t clean your tank filter more often than once a month, maybe, except for cases where the filter accumulates a lot of dirt and debris fast.

At the same time, most novice fish keepers are guilty of 3 major mistakes when cleaning the filtering system:

  • Being too conscientious about it – Your tank filter houses billions of beneficial bacteria responsible for consuming ammonia and nitrites and turning them into nitrates. Cleaning the filter too often or too thoroughly will kill off these bacteria, sterilize the tank’s biome, and do more harm than good in the process.
  • Using tap water or cleaning chemicals – Using chlorinated tap water is a surefire way of destroying much of the bacteria living in the filter. The same goes for relying on various sterilizing chemicals designed to kill every life form in the equipment, harmful or not.
  • Letting the filter out of the water for too long – The cultures of beneficial bacteria only survive in wet environments. Even a few hours out of the water will start killing them off fast.

The solution:

Clean the filtering system with tank water and only remove visible algae deposits, debris, and dirt.

Don’t be too thorough about it, don’t use cleaning chemicals, and don’t use chlorinated water in the cleaning process.

Most importantly, don’t keep the filter out of water for too long. Clean it and put it back into the tank. It doesn’t need drying; you will get it wet soon anyway.


Glofish need regular water changes depending on their aquarium setup, number of fish, and the species they belong to.

The most common problems that arise stem from people’s lack of knowledge regarding safe and effective water changes.

Learn the most common problems attributed to inadequate water changes. Learn how to prevent them, and your fish should be fine.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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