Why Are My Guppies Dying? (9 Steps To Fix It Quickly)

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Unfortunately, guppies that keep dying are a common issue these days. 

In many cases, despite your best efforts, the creatures die one by one as soon as you add them to the tank.

Since I suffered from this issue quite a bit in the past, I decided to dedicate an entire article, explaining how to diagnose the problem and fix it quickly.

Let’s dive right into it.

Also Read: Stress In Guppy Fish

Some guppies will lose their colors when stressed, starting at the abdomen.

Why Are My Guppies Keep Dying?

1. Inappropriate Cycling

Cycling is the biological maturation process of a new fish tank.[1] During this stage, which usually lasts six weeks, nitrifying bacteria will build up.

These vital bacteria will then consume ammonia produced by aquarium fish, and turn it into nitrite and ultimately nitrate, which is removed by plants, algae, and water changes.

If the tank is not cycled, ammonia and nitrites will kill your guppies shortly after you add them to the tank, possibly one by one on their first day.

You can take steps to neutralize the toxins. But in an uncycled tank, the toxins may spike faster and more frequently than you can react.

These signs suggest that your tank isn’t properly cycled:

  • You have recently started a brand-new fish tank.
  • Ammonia and nitrites are above 0 ppm but nitrates are at 0 ppm.
  • Algae have started building up on rocks, plants, and decorations.
  • Your dead guppies developed red or bleeding gills.

Cycled tanks will typically show 0 ppm of ammonia and nitrite, as there are enough nitrifying bacteria to break down these toxins.

Nitrates are formed in the last step of the cycling process, and usually indicate that the cycling process is now complete.

Solution #1:

  • Get rid of the water your guppies recently died in. 
  • Set up the aquarium by adding your filter, heater, substrate, and decorations. 
  • Add up to one guppy per 10 gallons of water. 
  • Be sure to feed your guppies small meals in the first six weeks. 
  • Measure the ammonia, nitrite, and nitrate every two days. If any of these toxins are above 0 ppm, do a partial water change (15-20%).
  • After four to six weeks, start feeding your guppies as much as they can finish in two to three minutes. 
  • If at this point the ammonia and nitrite remain at 0 ppm, and the nitrates remain below 20 ppm, your tank is cycled and you can add the rest of your fish.

Solution #2:

If you don’t want to wait six weeks, you should know that there is a faster way to cycle in a fish tank. You can simply transfer the filter media or substrate from an older aquarium.

This way, you’ll actually be transferring “pre-made” nitrifying bacteria instead of waiting for them to form naturally.

You can also use commercial products like the API Quick Start Nitrifying Bacteria (link to Amazon). Although I haven’t used it personally, some of my friends have seen great results with it:

2. High Ammonia, Nitrite & Nitrate

If your tank is already established, it’s probably cycled (especially if you’ve had it for a few months, and all your fish look healthy).

However, ammonia and nitrite are still generated in cycled tanks, only nitrifying bacteria immediately consume them, turning them into nitrate.

But if you add a large population of fish, such as a group of guppies, the balance may break and the bacteria will not be able to cope with the amounts of ammonia they produce.

Indeed, more bacteria will form in response to this scenario. But this process takes time, and unfortunately, your guppies will probably die in the meantime.

These signs indicate that your guppies died due to a spike in ammonia, nitrite, or nitrate:

  • Your tank is cycled but populated with a fair amount of fish.
  • You have significantly increased the amount of food or feeding frequency.
  • Other fish died besides your guppy.
  • You measured ammonia and nitrite levels above 0 ppm or nitrate of about 40 ppm.
  • Your guppies’ tails kept drooping.


Even if you’re sure your tank is cycled, it’s still best to add a group of guppies gradually. You don’t want to overload your tank or overwhelm your nitrifying bacteria.

Start with a pair of female guppies and see how they handle their environment. After a couple of days, if everything seems fine, add the rest.

Also, be sure to feed the new fish population the amount of food they can consume in two to three minutes, twice a day. Avoid overfeeding at all costs.

After a week or two, the feeding frequency can be increased to three times a day, while closely monitoring the ammonia and nitrite.

Vacuuming the substrate is one of the most important steps in fighting ammonia spikes.

3. The Wrong Male-To-Female Ratio 

Ideally, you should keep three females for every male guppy.[2] Keeping more males will end in harassment and stress.

If you tried to add an equal number of males and females or more males than females, your guppies probably died because of it.

Signs that your guppies died due to inappropriate male-to-female ratio:

  • The female guppies died first.
  • The males seemed to be bullying the females, as well as each other.
  • Your guppies have broken or torn fins.


Start by adding two to three females, keeping the males in another tank. This will allow the females to get used to their new environment.

Next, add the males while keeping the 1:3 ratio. Also, try not to add more than two males to the same tank, especially if it is 20 gallons or less.

4. Aggressive Tankmates

There are certain species you should avoid mixing with guppies:

  • Angelfish
  • Endler’s Livebearers
  • Barbs
  • Oscars
  • Goldfish
  • Killifhs
  • Flowerhorn
  • Discus

These signs typically suggest that your guppies died because of inappropriate tankmates:

  • Your aquarium contains at least one of the species mentioned above (or any other large and aggressive species, cichlids in particular). 
  • Your guppies started losing their tail, scales, and fins
  • You can see other fish attacking and chasing your guppy fish.


Choose suitable tankmates for guppies, such as:

5. Low Oxygen Levels

Guppies will die in a tank with low oxygen levels, especially if the aquarist in question fails to act quickly enough to resolve the problem. 

The oxygen in a stagnant tank will dissipate gradually until the guppies suffocate. These signs are usually associated with a lack of oxygen:

  • You recently added a large group of fish to your tank (be it guppies or other fish).
  • There is no agitation in your tank, no bubbles whatsoever.
  • Your guppies stayed at the top of the tank for extended periods before dying.
  • The guppies were breathing fast and heavily.[3]
  • Other fish in your tank died as well.
  • There is a large amount of vegetation and algae in your tank.


Fixing an oxygen deficiency is pretty straightforward. All you have to do is increase the agitation in your tank, allowing oxygen to dissolve from the surface.

When I had this problem before, all I did was install an airstone. I got the Hygger Aquarium Air Stone (Amazon link), which is incredibly quiet.

Just make sure to place it in a way where the bubbles can reach the surface. If plants or decorations block the bubbles, oxygen will not be able to enter.

Adding an airstone is the easiest and fastest way to increase the oxygen in your tank.

6. The Wrong Temperature

Guppies are considered hardy creatures, which is why inadequate temperature usually doesn’t kill them.

However, temperature fluctuations can stress your guppies, making them more susceptible to other conditions that could contribute to their death.

The ideal temperature for guppies is 72-82° F (22-28° C).[4] The temperature should also remain stable, without fluctuations of more than 0.5°.

Don’t assume that the temperature in your aquarium is acceptable simply because the tank has a heater. 

Heaters malfunction all the time. They will either raise the temperature or permit it to fall because they have stopped working.

7. Acidic Water (Low pH Levels)

Guppies typically enjoy a pH level ranging between 7.0 and 8.0. That is also the pH you find in most home aquariums, which is pretty standard.

However, in many cases, the pH can drop below 7.0, making the water too acidic for guppies. This usually happens in unmaintained tanks with elevated ammonia.

That is also a manifestation of an overpopulated tank with too many leftovers and debris.


  • Make a partial water change until the pH stabilizes between 7.0 and 8.0.
  • Siphon the substrate thoroughly.
  • Remove debris and leftovers seen on aquarium plants and decorations.
  • Consider lowering your fish population.

8. Genetic Issues

Some guppies have weak genetics. They are born with a shorter lifespan. You see this in bright and colorful variants that aquarists created through selective breeding. 

If all the dead guppies were born in your aquarium, you should start over. Cull the guppies and buy a brand-new breeding pair.

If all the dead guppies come from the same store, you should change suppliers. For all you know, the store’s entire stock of guppies has the same weakness.

Colorful guppies are more susceptible to genetic issues due to selective breeding.

9. Underlying Diseases

If other fish in your aquarium are dying as well, or if the guppies came from the same source, a disease could be involved. Some common illnesses in guppies include dropsy, velvet, fin rot, and flukes.

Sick guppies may become swollen, develop white patches, scratch against objects, swim erratically, and show no interest in food.

Pathogens associated with these illnesses include parasites, bacteria, and viruses. These can infect your water and attach to objects and plants.

For your convenience, here is an excellent Youtube video showing how to identify and treat the most common diseases in guppies:

What Are The Symptoms Of Dying Guppies?

Dying guppies tend to present typical symptoms, such as loss of appetite, lethargy, and rapid breathing. 

Some guppies will also become pale and start swimming erratically. These signs usually require immediate intervention. Otherwise, the guppy may die.

This is what you should look for:

1. Loss Of Appetite

This is one of the first things to go. Sick and stressed guppies will stop eating. First of all, you will notice that they no longer respond to the food you add to the tank. 

Secondly, the volume of leftovers in the tank will increase, showing you that the guppies have no interest in food. 

Fish cannot survive without food. If a guppy has stopped eating, it will eventually die.

2. Color Changes

Guppies usually have beautiful colors. If your guppy is losing its color, you should worry. Sick guppies usually look dull, sometimes turning white entirely.

You see this primarily in males, which usually present intense colors to attract females.

Just before they lose their colors, you may see their eyes turning black. That is a typical sign of stress in guppies.

3. Lethargic Swimming

Dying guppies will stop moving altogether. And whenever they move, their motions are sluggish. The males will also stop going after the females as they usually do.

In some cases, you will find your guppy floating motionless at the bottom of the tank or slowly swimming up and down vertically.

4. Rapid Breathing

Like most fish, guppies extract oxygen from the water to survive. One common sign of impending death in fish is labored breathing. 

Because guppies need oxygen to survive, any condition that compromises their ability to breathe will kill the creatures. 

Some guppies will choose to swim at the top, where the water holds more oxygen. Either way, you’ll see the gills moving faster than usual.

A diseased, deformed guppy that stays at the top to get more oxygen.

How To Revive A Dying Guppy

If the guppy is still alive, you can use the following steps to keep the creature from dying:

  • Perform a partial water change. A water change improves oxygen levels, ejects parasites, reduces toxin levels, and so much more. It can deliver immediate relief.
  • If your guppy is too weak to survive a water change, but the tank has too many toxins, apply water conditioners to neutralize those toxins within minutes.
  • Make sure the guppy is well-fed. Add a mixture of animal and plant matter. 
  • Maintain a proper day/night cycle. Leaving the lights on 24 hours a day will stress them because they can’t rest. Remedy the issue by giving them 8 hours of darkness at the end of the day.
  • If you suspect that your guppy is sick, follow the instructions below.

Sometimes, it can be challenging to identify the specific disease your guppy caught, especially if you have no previous experience.

So, when in doubt, my general rule of thumb is to use the Tetra Lifeguard® (link to Amazon).

Guessing what disease is causing the issue can be time-consuming, and while you are pondering, your fish’s condition will probably deteriorate.

That is why starting treatment with Lifeguard is a wise choice. It’s a non-antibiotic agent that covers many illnesses, including:[5]

  • Ich
  • Red streaks
  • Milky or shedding slime
  • Flukes
  • Bacterial gill disease
  • Mouth and fin rot
  • Clamped or torn fins
  • Ulcers

Here are the instructions:

  1. Isolate your sick fish and move it to a hospital tank.
  2. Remove filter carbons and turn off any UV sterilizers.
  3. Add one tablet per day to every 5 gallons.
  4. Treat for five consecutive days.
  5. Repeat the process until the symptoms clear.

Also Read: Guppy Laying At The Bottom


For your convenience, here is a simple checklist you can follow to prevent your guppies from dying:

  • Make sure that your tank is fully cycled (the desired point is ammonia and nitrite at 0 ppm and nitrate below 20 ppm)
  • Measure the ammonia, nitrite, and nitrate after a few hours of adding your guppies, and make a partial water change if necessary.
  • Pick three females for every male (3:1 ratio).
  • Make sure there are no aggressive species in your tank, with cichlids and large fish in particular.
  • Install an airstone if there is no agitation in your tank.
  • Adjust the temperature to 72-82° F (22-28° C).
  • Keep the pH between 7.0 and 8.0.
  • Pick your guppies from a reputable source (preferably from more than one supplier).
  • Don’t hesitate to use the Tetra Lifeguard if you noticed some signs of illness.


  1. https://www.thesprucepets.com/speed-up-aquarium-cycle-1380707
  2. https://www.aquariumnexus.com/guppy-male-female-ratio/
  3. https://www.thesprucepets.com/low-oxygen-in-aquarium-water-1381215
  4. https://japanesefightingfish.org/guppy-temperature/
  5. https://www.tetra-fish.com/products/water-care/lifeguard-tablets.aspx