Why My Guppy Died Suddenly? (9 Reasons+Prevention)

When keeping guppies, we sometimes encounter our guppy fish dying suddenly overnight. There can be numerous reasons and essential prevention behind such issues. So, Why my guppy died suddenly? Let us find out.

Poor water quality and a non-cycled tank are the primary reasons your guppy died suddenly. Other reasons are overcrowded tanks, overfeeding, and bad genetics. Ensure cycling your new tank and providing your guppies with good quality water to prevent them from such issues.

This article will discuss all the reasons and prevention for guppy fish dying suddenly. So, let us get into it.

My Guppy Fish Died Suddenly.

Guppy fish can die suddenly because of numerous reasons, of which a non-cycled tank is a primary reason behind that.

Other reasons are poor water quality, inadequate water parameters, a spike in ammonia, and the genetics of guppy.

The non-cycled tank will not have beneficial bacteria to eliminate toxic chemicals, resulting in guppy fish passing away suddenly.

Let us discuss all the reasons behind guppy fish dying suddenly.

What are the reasons behind my guppy fish died suddenly?

These are the reasons behind your guppy fish died suddenly:

  1. Your tank is not cycled.
  2. Your guppies aquarium water quality is poor.
  3. The water temperature of your guppies aquarium is inadequate and unstable.
  4. Your guppies aquarium water contains high ammonia.
  5. Your guppy was suffering from disease or parasite.
  6. Your guppy is overfeeding.
  7. Your guppies tank is overcrowded.
  8. The genetics of your guppy fish is poor.
  9. Your guppy’s aquarium water lacks oxygen.

The guppies tank is not cycled.

Non-cycled tank is the primary reason behind your guppy fish dying suddenly.

When we buy a new aquarium, we have to cycle our tank to colonize beneficial bacteria in our aquarium system.

The beneficial bacteria help eliminate harmful chemicals like ammonia and nitrite from your guppies tank.

Without performing a nitrogen cycle, beneficial bacteria will not develop, and there will be a spike of ammonia and nitrite, resulting in your guppy dying overnight. 

Poor water quality

Poor water quality can make your guppy fish pass away suddenly.

Contaminated water will result in a spike of harmful toxins like ammonia in the water.

There will also be a lack of oxygen in contaminated water, making your guppy suffer, and they can pass away suddenly.

Inadequate and unstable water parameters

Inadequate water parameters can also make your guppy fish pass away suddenly.

Your guppy fish will come under stress when living in an inadequate water temperature.

The too high temperature will boost your guppy’s metabolism, making them hyperactive. 

Hyperactive guppy fish will swim erratically and will come under stress.

The too low water temperature will make your guppy fish lethargic and lose their appetite. 

Your guppy fish will come under stress and can pass away suddenly.

A low pH level (Below 5) will make your guppy’s water acidic, burning their gills and skin, and your guppy can suddenly pass away. 

Also, you must know that with inadequate water parameters, stable water parameters can also be the reason for your guppy fish passing away suddenly.

Also read: What Is The Ideal Water Temperature For Guppies?

Spike of ammonia

A Spike of ammonia can also make your guppy fish pass away suddenly.

Usually, ammonia occurs in a new tank.

However, ammonia can also occur in old tanks because of the following reasons:

  1. When you add much fish at one time.
  2. The beneficial bacteria pass away.
  3. When your filtration system doesn’t work properly, ammonia will occur.

Your guppy will not be able to eat efficiently and will become lethargic, resulting in passing away suddenly.

Diseases and parasites

Your guppy fish can pass away suddenly because of disease or parasite.

The primary reasons for various diseases and parasites are poor water quality and genetics.

Your guppy can get sick by disease and parasite and can pass away.

The most common diseases in guppies are ich, fin rot, and flukes.


Overfeeding your guppies can also make them pass away suddenly.

Your guppy fish can suffer from constipation and will become lethargic.

Overfeeding guppies will pollute the water from the guppy’s leftovers. 

There will be a spike of ammonia and deficiency of oxygen from which your guppies can come into critical condition and pass away.

Also read: Can Guppy Die From Overfeeding?

Overcrowded tank

The overcrowded tank will result in all these things:

  1. Your tank will get polluted faster than usual.
  2. There will be a lack of oxygen in your guppies aquarium.
  3. Your guppy will not be able to swim and live comfortably.
  4. Your guppy will come under stress.

All the above reasons can make your guppy fish pass away. 

Poor genetics

Guppies from weak genetics can pass away suddenly.

When you buy guppies from a pet store, it is always possible that the genetics of that guppies are bad.

Guppies with bad genetics will easily get prone to various diseases and parasites.

Also, guppies with bad genetics will have a shorter life span.

So, always consider buying guppies from a trusted breeder who bred healthy guppies.

Lack of oxygen

Lack of oxygen in your guppies aquarium can also suddenly make your guppy pass away.

Your guppy fish will become lethargic as they need oxygen for their movement.

Your guppy will gasp for air at the surface of the water.

Also, you must know that beneficial bacteria present in your guppies aquarium will require oxygen to eliminate ammonia and nitrite.

And, when there is no oxygen, beneficial bacteria will not be able to eliminate ammonia, making your guppy’s water quality poor, and your guppies can pass away suddenly.

How to prevent guppy fish from dying?

Perform these things to prevent your guppy fish from dying:

  1. Cycle your new tank.
  2. Provide good water quality to your guppies.
  3. Avoid overcrowding your guppies tank.
  4. Avoid overfeeding your guppies.
  5. Perform regular tank maintenance.
  6. Add compatible tankmates to your guppies aquarium.

 Cycle your new tank

Whenever you buy a new tank, make sure to perform a nitrogen cycle first before adding guppies.

Performing the nitrogen cycle will help you develop beneficial bacteria in your aquarium.

Beneficial bacteria will help convert ammonia into nitrite into nitrate.

This process will take some weeks but performing a nitrogen cycle is essential.

The best method to cycle your guppies tank is fish-less cycling.

In this method, you have to introduce ammonia to your guppies tank.

You can do this by adding fish food to your guppies tank.

The best thing about this method is that no fish is needed in your aquarium to complete the cycle.

Only ensure to add ammonia continually so that the bacteria don’t pass away because of lack of food. 

Once the cycle is completed, start adding fish slowly to keep the cycle going. 

Also read: My Guppy Died After A Water Change.

Provide good water quality

Ammonia spike occurs typically in a new tank but can also occur in an established tank if the water is contaminated.

Also, poor water quality will lack oxygen, and your guppies will suffer.

To ensure good water quality, perform a weekly water change of 30%.

Also, consider adding a good filtration system to keep the water clean and away from harmful chemicals. 

Avoid overcrowding

Your guppy fish will not be able to swim comfortably in an overcrowded tank. 

The overcrowded tank will also have oxygen deficiency, resulting in your guppy fish passing away suddenly.

Follow the one-inch per-gallon rule to ensure that you are not overcrowding your guppies tank, which means one inch of fish per one gallon of water.

This way, you will not overcrowd your guppies tank.

Also read: How Many Guppies In A 20 Gallon Tank?

Avoid overfeeding

Overfeeding your guppies can make your guppy suffer from a life-threatening condition. 

Your guppy can suffer from constipation and also can pass away suddenly.

To ensure you are not overfeeding your guppies, provide them food in a quantity that they finish in 1 minute. 

Feed your guppies once or twice a day. 

Guppy FoodServing QuantityNo of Times
Veggie pelletsOne small pinch at a time2-3 times a day
Brine shrimpOne small pinch at a time1-2 times a week
BloodwormsOne small pinch at a time1-2 times a week
Tubifex WormsOne small pinch at a time1 time a week
Mosquito larvae10-15 pieces2-3 times a week
This table shows the dietary requirement of guppy fish.

Also read: Best Food For Guppy Fish.

Perform regular tank maintenance

Performing regular tank maintenance is equally important to prevent your guppy fish from passing away.

You should clean your guppies aquarium and filter once a month to get rid of excess waste. 

Ensure not to clean the sponge and biofilter media with tap water as it will destroy all the beneficial bacteria. 

Also, don’t dry out the sponge and biofilter media as it will also eliminate beneficial bacteria.

Clean the sponge and biofilter media with the aquarium water. 

You can also siphon the substrate once a month to extract the waste from your guppies aquarium. 

Add compatible tankmates 

Guppies are peaceful fish and do great with other peaceful fish in a community tank.

Adding aggressive fish like angelfish will stress out your guppy fish.

Aggressive fish will constantly chase and nip your guppy fish fins, making them come under stress.

Because of constant chasing, guppy will become weak and lethargic, resulting in sudden passing away.

You must know that constant stress will make your guppy fish prone to diseases and parasites.

Consider adding similar size peaceful fish to your guppies aquarium.

These are some best tankmates for your guppies:

  1. Mollies
  2. Platies
  3. Neon tetra
  4. Gourami
  5. Shrimp
  6. Zebra danios

Also read: Can Guppy Fish Live With Angelfish?


Non-cycled tank and poor water quality is the primary reason behind your guppy fish dying suddenly.

There are other reasons, like, overfeeding, overcrowding, bad genetics, and an ammonia spike.

Provide your guppy fish with good water quality by performing a weekly water change and adding a good filtration system with biofilter media to prevent your guppy fish from dying.

Avoid overfeeding, overcrowding, and buying guppies from a well-known breeder to prevent such issues.

Also, make sure to perform a nitrogen cycle when you buy a tank before adding guppies.

Reference: JSTOR

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