Why Are My Guppies Lethargic? (Reasons+Prevention)

Guppies are the most common fish every aquarist prefers to add to their home aquarium. They can live in a wide range of water parameters and are not high maintenance, making them a perfect fish for beginners.

However, guppies sometimes show strange behavior, which makes us worry. One of them is guppy, being inactive and not moving much. Let us know the reason behind such an issue. So, Why is my guppy lethargic? Let us find out.

Poor water quality is the primary reason for your guppy being lethargic. However, other reasons are overcrowded tanks, bullying, and inadequate water parameters. Consider doing a weekly water change of 30%, avoid overcrowding tanks, adding aggressive tankmates to prevent guppy from such an issue.

This article will discuss all the reasons and prevention of guppy fish being lethargic. So, let us get into it.

My guppy fish is affected by lethargy.

There can be numerous reasons for your guppy fish becoming lethargic, of which the poor water quality is the primary reason.

Poor water quality lacks oxygen which guppies need for their movement and survival.

And because of lack of oxygen, guppies prefer not to move much and become inactive to preserve energy.

There can be other reasons, like aggressive tankmates, inadequate and unstable water parameters, and overcrowded tanks.

Let us discuss all the reasons behind guppy fish being lethargic.

What are the reasons behind my guppy fish being lethargic?

These are the reasons behind your guppy fish being lethargic:

  1. The water quality of your guppies aquarium is poor.
  2. Oxygen is Deficient in your guppy’s aquarium water.
  3. The water parameters of your guppies aquarium are not adequate and stable.
  4. Your guppy is being bullied.
  5. There has been excessive use of liquid fertilizer.
  6. Your guppies aquarium is overcrowded.
  7. You are overfeeding your guppy fish.
  8. Your guppy is suffering from a disease or parasite.

Poor water quality

Poor water quality is the primary reason behind your guppy fish being lethargic.

Poor water quality can result in these things:

  1. Spike of ammonia and nitrite.
  2. High nitrate level.
  3. Stress.
  4. Deficiency of oxygen.

All the above reasons will make your guppy fish lethargic.

Spike of ammonia and nitrite

Poor water quality will result in a spike of ammonia and nitrite.

When the ammonia and nitrite get a spike in your guppies aquarium, your guppies will be affected in various ways:

  1. Your guppy will gasp for air.
  2. Your guppy fish will lose its appetite.
  3. Your guppy fish will be lethargic.

High Nitrate level

Where there will be a spike of ammonia and nitrite, there will also be a high nitrate level.

High nitrate levels will result in algae growth, and the oxygen level will also get deficient in an aquarium with high nitrate levels.

You must know that high nitrate levels will make your guppy fish prone to various diseases and parasites and make your guppy fish lethargic.


Poor water quality will make your guppy fish come under stress, and they will become lethargic.

Poor water quality will cause deficient oxygen, and your guppy fish will struggle, making them come under stress.

Also read: Are My Guppies Stressed?

Deficiency of oxygen

Poor water conditions will result in a deficiency of oxygen.

You must know that the beneficial bacteria present in our guppies aquarium requires oxygen to break down harmful toxins like ammonia and nitrite.

And in the absence of oxygen, beneficial bacteria will not be able to eliminate ammonia and nitrite from your guppies aquarium, and your guppy will become lethargic.

Lack of oxygen in your guppies aquarium

Numerous reasons can result in a lack of oxygen in your guppies aquarium:

  1. Poor water quality
  2. Algae growth
  3. Plant overgrowth
  4. Overcrowded tank

Your guppy fish will suffer and spend most of the time at the water’s surface gasping for air.

Also, your guppy will not move much and become lethargic as they will preserve energy for their movement.

Inadequate and unstable water parameters

Inadequate and unstable water parameters will also result in your guppies becoming lethargic.

Guppies are tropical fish and prefer to live in warm water. 

Too cold water will make your guppy fish inactive and lethargic.

Also, unstable water parameters will make your guppy fish come under stress, and they will become lethargic.

Guppy fish don’t prefer to live in acidic water and can come into critical conditions living in acidic water.

Fall in pH level will stress out your guppy fish, and you must know that a very low pH level will burn out your guppy’s skin and gills, making your guppy pass away.

Also read: Best pH level for guppies.

Bullied Guppy

Chasing and bullying are normal in guppies until and unless it becomes a habit of your guppies.

Bully can happen in an overcrowded tank, male-only tank, aggressive tankmate.

Bullying happens for food, mating, and forming a hierarchy.

Male guppies are more aggressive when no female guppy is present in your guppies aquarium.

Also read: What To Do If My Guppy Is Stressed?

Excess use of liquid fertilizer

Usually, Liquid fertilizers are good for live aquatic plants as they provide the required nutrients to them. 

Liquid fertilizer is also not harmful to guppies and invertebrates like snails.

However, excess liquid fertilizer will affect your guppy’s health, which can come under stress.

Overcrowded tank

An overcrowded tank will also result in your guppy fish becoming lethargic.

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

Also, an overcrowded tank will lack oxygen, and your guppy fish will suffer.

All these will make your guppy fish come under stress, behaving inactively.


Overfeeding your guppy will also result in making your guppy fish lethargic.

Guppies are ravenous eaters and will eat every time you serve them, whether they are hungry or not.

Guppy keepers usually get confused by such eating behavior of guppies and end up overfeeding them.

Overfeeding will make your guppy fish constipated, bloated, and lethargic.

Also, it will pollute the water by fish leftovers, resulting in a lack of oxygen, and your guppy will suffer.

You must know that constipation and bloated belly issues can become a life-threatening conditions for your guppies if not treated early. 

Also read: Can Guppy Die From Overfeeding?

Guppy is suffering from diseases and parasites.

There are various diseases and parasites from which your guppies can be prone if not kept in an ideal tank condition.

Guppy fish suffering from any disease and parasites will show hiding behavior and become lethargic and less active. 

Some symptoms of guppy fish suffering from diseases and parasites are:

  1. Your guppies fin will rot.
  2. There will be white spots on your guppies body and fin
  3. Your guppies will have red-blooded gills.

Detecting the disease and starting the treatment in the early stages is essential to ensure a fast recovery.

You should first isolate the sick guppy fish to ensure that the other fish remain safe if you detect any disease or parasite.

After isolating the sick guppy, run the proper treatment, including antibiotics, regular water change, adequate tank maintenance, and Regular feeding of nutritional food.

You will also need to increase the oxygen level by adding live aquatic plants or agitating the surface area by adding an air pump. 

How to Prevent your guppies from being lethargic?

Perform these things to prevent your guppies from becoming lethargic:

  1. Provide good water quality to your guppies.
  2. Avoid overcrowding your guppies aquarium.
  3. Avoid adding non-compatible tankmates to your guppy tank.
  4. Provide your guppy with their ideal water parameters.
  5. Maintain male and female guppies ratio.

Provide good water quality

Providing good water quality will prevent your guppies from becoming lethargic.

You can ensure good water quality by performing a weekly water change of at least 30% of your guppies aquarium.

Performing a regular water change will help eliminate the ammonia and nitrite from your guppies aquarium.

Also, add a good filtration system with biofilter media to keep your water clean and oxygenated.

Adding live aquatic plants to your guppies aquarium will also help keep the water clean and well oxygenated.

If you are using liquid fertilizer to fulfill the nutritional requirement of plants, ensure using it only once a week.

Make sure to maintain ammonia and nitrite at 0ppm and nitrate at below 25ppm.

Avoid overcrowding your guppies tank.

An overcrowded tank will make your guppy fish come under stress and become lethargic.

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

Following this rule will ensure that you are not overcrowding your guppies aquarium.

The overcrowded tank will lack oxygen, and it can result in a spike of toxic chemicals like ammonia and nitrite, so always consider not overcrowding your guppies tank. 

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

Avoid adding non-compatible tankmates.

Adding non-compatible tankmates like aggressive fish and big-sized fish will stress your guppy fish.

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

Guppy fish will hide from aggressive tankmates most of the time and will not eat properly.

All this will result in guppy losing its appetite becoming weak and lethargic.

So, consider adding compatible tankmates of guppy fish to your guppies aquarium.

These are some best tankmates of guppy fish:

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

Consider peaceful and similar size fish for adding to your guppies aquarium.

Also read: Can Guppy Fish Live With Angelfish?

Provide adequate water parameters to guppies.

With good water quality, adequate water parameters are also equally essential to prevent your guppies from becoming lethargic.

ParticularsGuppy Fish Requirement
Water temperature72-82 °F
Water pH level6.8-7.8
This table shows the ideal water parameters of guppy fish.

Guppy fish require a water temperature between 72-82 °F to thrive.

The water pH level of your guppies aquarium water should be between 6.8-7.8.

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

Maintain male and female guppy ratio.

Maintaining the male and female guppy ratio is essential to prevent your guppy from being bullied and coming under stress.

More male and few female guppies will result in male guppy constantly chasing particular female guppy for mating.

Only male guppy will result in male guppy being aggressive and more territorial.

So, consider keeping guppies in a ratio of 1:2, which means one male guppy and two female guppies.

You can also keep one male guppy and three female guppies.

This way, the stress because of the constant chasing of male guppy for mating will get distributed among all the female guppies, and each will get time to calm down.

Also, there will be no aggression because of only male guppy in your guppies aquarium.


There are numerous reasons behind guppy fish becoming lethargic, of which poor water quality is the primary reason.

Other reasons are aggressive tankmate, overcrowded tank, deficiency of oxygen, and inadequate and unstable water parameters.

Poor water quality will lack oxygen, and guppies will suffer as they require oxygen for movement and survival.

Consider performing a weekly water change of 30% and adding a good filtration system to ensure the good water quality of your guppies aquarium.

Also, make a stress-free environment for your guppies by avoiding aggressive tankmates, overcrowded tanks, and unstable water parameters.

Reference: NCBI

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