how to clean a fish tank after a fish has died

How To Sterilize A Fish Tank After A Fish Died

(Last Updated On: May 23, 2021)

Keeping a fish tank clean is essential. Improper conditions cause several problems, affecting the tank’s eco-system and surviving fish. So, you’ll need to know what to do when a fish dies in your aquarium.

When a fish dies, the tank should be sterilized to prevent poor water conditions and contagious diseases from being passed to healthy fish. A 10-20% water change should be enough if the ammonia levels are stable. To thoroughly clean the tank, make a solution of one part bleach and one part water and scrub the tank, including artificial plants and removable, non-porous items.

When you have lots of plants and decorative features in the tank, dead fish aren’t always easy to spot and remove. So, keep a close eye on your tank’s conditions for any changes. If the ammonia levels rise without an apparent reason, one of the fish has likely died, and the aquarium needs sanitizing.

How To Clean A Fish Tank After A Fish Has Died

Even if only one fish dies and the others seem fine, you should clean the tank in case the fish died of a parasite or contagious disease.

If the tank’s ammonia and nitrite are at a safe level, you may not need to do a deep sanitization. However, you’ll still need to check the aquarium’s cleanliness using testing strips or a similar device.

To clean and sterilize your aquarium after one of your fish has died, follow these steps:

Remove The Dead Fish

Once you notice a dead fish in your tank, you must remove it as quickly as possible to prevent the conditions from deteriorating.

Similarly, if your fish died from a disease or bacterial condition, the rest of your tank is at risk. There might be instances when you notice a fish is missing, but you can’t find its body. This is likely because:

However, where there’s a body, put on plastic gloves and scoop the dead fish out of the tank with a net, placing it into a plastic bag.

Your first instinct might be to flush the deceased fish down the toilet. However, this isn’t a good idea, as dead fish can block the soil pipe network.

You could place the fish in a waste bin. However, on a hot day, the fish will attract flies and other bugs, causing unsanitary conditions. While it’s the easiest way to dispose of your fish, avoid throwing your fish in the garbage if it’ll be sitting there for a few days.

Alternatively, you could bury the fish in the yard. This way feels more personal and is more hygienic than other disposal methods.

what to do when a fish dies in your aquarium

Check The Ammonia Levels

Depending on how long the fish has been decomposing, the ammonia within the tank could rise to dangerous levels. Smaller tanks will experience rising ammonia quicker than a tank with a larger surface area.

For example, a 30-gallon tank could last the entire day before the water needs a complete change. In contrast, a 5-gallon tank will become polluted in only a few minutes.

Ammonia is dangerous to fish and causes severe health problems. If your tank’s ammonia and nitrite levels are too high, you’ll need to disinfect the tank and replace the water.

If they’re at a normal level, you can get away with doing a standard water change. You can test ammonia levels using a liquid water test kit or test strips.

Change The Water

As we’ve already mentioned, a water change is sufficient to sanitize the tank if one of your fish has died but the decomposing body hasn’t affected the water’s chemical balance.

When other healthy fish are in the tank, it’s not advised to drain the water, as you’ll need to re-cycle the entire aquarium. This takes time and puts the fish at risk.

Instead, carry out a water change as soon as you realize one of your fish has died, replacing 10-20% of the tank’s water. This should get the ammonia levels under control. To do a water change, follow these steps:

  1. Remove the water using a jug, pouring the water into a bucket.
  2. Scrub the tank’s sides using an algae brush or magnet to remove bacteria and algae.
  3. Remove the artificial plants and ornaments and scrub them with the same algae brush.
  4. Siphon out any waste that has settled on the substrate.
  5. Clean out the filter, swooshing it in the tank’s water to keep all the beneficial bacteria.
  6. Add clean water to the tank and add a dechlorinating solution, following the instructions carefully.

While you shouldn’t use bleach in a tank containing healthy fish, you might want to remove all the decorations and small parts to sanitize them with a bleach solution. This will ensure they’re not harboring harmful bacteria.

Disinfect The Tank

If the tank’s water quality has deteriorated because of the dead fish, you’ll need to thoroughly disinfect the tank to remove all traces of bacteria, disease, and ammonia if all of the fish inside your tank has died.

According to the Journal of the American Association for Laboratory Animal Science, laboratories studying fish must be cleaned and disinfected to minimize the spread of pathogens and build-up of waste products.

You should apply the same level of thinking when cleaning your own tank.

A natural vinegar solution is sufficient for a standard aquarium sanitation. However, if your fish were struck down by sickness or disease, you’ll need to use bleach as it’ll kill pathogens.

Follow these methods for a clean, sanitized tank:

Bleach Solution

Standard household bleach is powerful enough to sanitize the tank against bacteria and germs. Similarly, don’t use bleach mixed with other detergents, as it could corrode your tank. To clean inside the tank, you’ll need a spray bottle. Tank components that are safe to clean with bleach include:

  • Aquarium; glass and Plexiglas
  • Filter hoses
  • Non-porous parts
  • Artificial plastic plants
  • The substrate, including gravel and rocks

Before cleaning, create a solution of 8 parts water to 1 part bleach. Use warm water to allow the bleach to dissolve Then, follow these steps:

  1. Remove your surviving fish into a separate tank.
  2. Put the bleach solution into a standard spray bottle. Spray inside the tank and leave the bleach to sit for 10 minutes, keeping a close eye on it to prevent corrosion.
  3. If your tank is particularly grimy, fill the entire aquarium with your bleach solution, using the 8:1 rule. Again, let it sit for 10 minutes.
  4. With both methods, rinse the tank thoroughly and let it air dry for 24 hours.
  5. Once the tank is dry, fill it with water. Add a dechlorinator to purify the water and leave it for a couple of hours.
  6. Empty the tank for a final time and re-add the dechlorinator to the fresh water.

After you’ve followed all of these steps, your tank is ready. However, remember to scrub all ornaments and decorative features using the bleach solution and a small brush to get into all the nooks and crannies.

The most important thing is to rinse the bleach off thoroughly to prevent your new fish from getting chemically poisoned.

Vinegar Solution

Bleach is corrosive and risks ruining your tank if it isn’t applied correctly. As a result, you can clean the tank using a natural vinegar solution – as long as your fish died naturally and not because of a disease. To do so, follow these steps:

  1. Remove your fish into a separate tank.
  2. Create a solution of one part water to one part white vinegar.
  3. Take all decorations and removable parts out of the tank and soak them in the solution.
  4. At the same time, fill the entire tank with the vinegar solution.
  5. After a couple of hours, remove the water from the tank and remove the removable items from the solution.
  6. Rinse everything thoroughly. If you notice some items still have buildup, make a stronger solution using two parts vinegar to one part water and leave it to soak for a little longer.

Because white vinegar is less corrosive than bleach, you can afford to soak your items for as long as you need to.

What Tank Problems Do Dead Fish Cause?

As you’d expect, dead fish cause sanitation problems, which can quickly escalate if the fish isn’t removed from the tank quickly enough. Once the following problems kick in, the tank needs a deep clean to sanitize it from harmful chemicals and pathogens.

High Ammonia Levels

If your fish tank is cloudy after your fish died, it’s likely because the ammonia levels have risen too high. It’s also the sign that a dead fish has been inside the tank for too long. Cloudy water is the result of bacteria bloom, which indicates an imbalance of bacteria.

In a tank with normal conditions, beneficial bacteria take care of the tank’s ammonia. Similarly, live aquarium plants absorb ammonia and nitrite compounds, using them as a food source.

However, when a fish dies, the body releases too much ammonia, which neither the bacteria nor the plants can control. If this is left to continue, fish become poisoned by the ammonia. Symptoms include:

  • Infections
  • Blindness
  • Recurring sores
  • Compromised immune system
  • Difficulty breathing
  • Torn fins

Therefore, you must remove dead and decomposing fish immediately.

Disease Transmission

Many fatal fish diseases are contagious and can affect all other fish in the tank, even after the host fish has died. Many parasites leave the fish in search of another host to infect, eventually causing the entire community to succumb.

Disease-causing bacteria and parasites will only exit the tank with a deep clean and sanitization. A simple water change is unlikely to be enough to save your fish. Contagious diseases include:

Similarly, some fish cannibalize their dead kin. As a result, they could get sick from the rotting flesh and pick up any diseases the fish is carrying.

do fish get lonely if one dies?


When dead fish are left floating in the tank, other fish sometimes become stressed by the dead body.

According to a paper by the Journal of Ethology, researchers discovered that fish form an attachment to their tankmates in as quickly as ten days. As a result, while fish aren’t likely to grieve, they may be able to recognize the death of a familiar. Physical signs of stress include:

  • A change to coloration, whether it becomes darker or lackluster
  • Unusual red streaking on the fins
  • White spots on the body, which is the sign of a parasitic or fungal infection

Behavioral signs of stress include:

  • A loss of appetite 
  • Darting randomly across the tank
  • Heavy breathing
  • Gasping for air
  • Hiding for long periods of time
  • Lack of activity
  • Scraping against the tank’s bottom
  • Strange swimming patterns

Similarly, dead fish cause the tank’s conditions to deteriorate, which is another reason for stress. There’s also reason to believe that fish know when another fish has died, which is also stressful.

Keeping your fish’s tank clean and sterilized is vital to keeping your surviving fish happy and healthy, especially after a fish has died. The reality is, you might not know what caused the fish’s death, meaning that the water could be compromised.

If you have lots of plants and hiding places in the tank, keep an inventory of your fish and try to do a regular headcount to determine whether any have died. Similarly, always check your aquarium’s ammonia levels in case they start to rise.