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9 reasons why your Guppies are dying (and how you can save them)

Guppies used to be known as hardy with an expected lifespan of up to 3 years. Due to an abundance of interbreeding and mass production to create fancy looking variants, however, this fish species is now considered to be more sensitive and, there, will live much shorter than ever before.

This guide at Aquarium Blueprints is going to help identify the most common causes of Guppy deaths as well as provide some tips of keeping your pets alive.

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About Guppies

Guppies are one of the most popular fish in the aquarium hobby as pretty much every fish store will sell them. This is because they can be extremely colorful with beautiful fins. Not to mention that they are very easy to breed as, most of the time, you only need a male and female to trigger spawning. They have the scientific name of Poecilia Reticulata in addition to also being referred to as the Million Fish.

Reason #1: Weakened Genetics

The main issue when it comes to the shorter lifespan of Guppies, especially when it comes to the fancier types, is the weakened genetics. This particular fish species is known for its wide variety of colors and fin types. In order to consistently produce these variants to be sold for profit, sellers have to resort to inbreeding by mating closely related fish.

A side effect to this practice is that the new generation becomes progressively less genetically diverse when compared the previous generation. As a result, the new-gen fish are more prone to diseases as well as genetic deformity (such as bent spine).

Solution #1:

If you don’t have any Guppies currently but are planning to keep some in the near future, the first step is to avoid buying fish with weak genes. To do so, you should look at sellers who practice line breeding.

With this method, the same strain of Guppies are kept in separate tanks. After three generations of inbreeding in the same tank, a fish one tank can then be added to the other tank. When done properly, this method is able to keep the desired visual traits going for future generations while also keeping the gene pool diversified.

So before buying Guppies, make sure you ask the sellers how the fish were bred.

Solution #2:

The other solution to weak Guppy genes is to simply breed your own colony. This requires you to keep both males and females. If you want the babies (also known as fry) to look like their parents, then you have to get both males and females from the same strain. If you don’t care how the offspring will look, then we recommend mixing different strains to add more even genetic diversity to the colony.

If you decide to use the same strains, you can keep two groups of the same Guppy strains in two separate tanks. After three generations of breeding, which usually take around a year, you can then take one male from Tank #1 and add it to Tank #2. You can then take one female from Tank #2 and add it to Tank #1. Keep in mind that both the male and female you are planning to move must be from the third generation; otherwise, you will end up with weaker genes than anticipated.

If you don’t want to use multiple tanks, a simpler solution is to simply add a new Guppy from the same strain into your aquarium every year.

If you are planning to breed healthy Guppies, you should also think about culling. If you want to keep your colony vigorous in the long run, you may want to remove any fish that have visible issues such as bent or curved spines. This is because there is a possibility that the same unhealthy traits will be passed to future generations.

To cull, you simply remove the undesirable fish from the tank. What you do with that fish afterwards is up to you.

Reason #2: Stressed Females

If you decide to breed Guppies, make sure you have the right ratio of males to females. This is because the males will chase the females around non-stop looking to pro-create. By being constantly being pursued, the females will be worn out and may succumb to illness and possibly death.


To prevent your female Guppies from dying due to being chased around, we recommend keeping a ratio of at least two females for every one male in your tank. That way, the male have multiple targets to pursue, which will give the other female some needed rest.

We also recommend adding live plants, as well as driftwoods and caves, to give your females places to hide and rest.

Reason #3: Low Fry Survival Rate

While breeding Guppies are extremely easy, keeping the fry alive may be tough in some tank setups. The most common causes for Guppy fry death is being eaten by bigger fish.

Solution #1:

The first solution is to simply separate the fry from the adult fish. To do so, we recommend moving the fry to a separate tank. You can then let them grow out until they are big enough to not get eaten by the adult fish in the original tank.

As an extra precaution, you may also want to move any fry that are growing much faster than the others as the bigger fry may eventually prey on their smaller siblings.

Solution #2:

You can also keep the fry and adult fish in one tank although the survival rate won’t be nearly as high. To increase the chances for the babies to survive, we recommend adding a lot of live plants. Not only will the plants provide hiding spaces, the fry will also eat the microorganisms that grows on the leaves and stems.

A floating plant like Hornwort and Java Moss has worked well for us. Make sure you put some at the top of the tank as the fry like to occasionally do near the water surface, which will leave them expose for being eaten. If you are interested, you can purchase our recommend Guppy fry saving plants on Amazon with the following links:

You should also keep both your adult and fry well fed. This will not only prevent the adults from trying to eat the fry (as their stomachs will be full), but will also help your babies grow faster in size.

Reason #4: Aggressive Tank Mates

Your Guppies could also be dying due to their tank mates. Other fish species may harass or attack Guppies, which may cause stress, injury and, eventually, death. Bigger fish species may even see the smaller tank mates as snacks.

Solution #1:

The most obvious, and best, solution is to get rid of the tank mates. You should only keep Guppies with peaceful fish of similar sizes. We consider the following fish species to be completely safe as tank mates:

  • Aquarium Snails
  • Corydoras
  • Kuhli Loaches
  • Mollies
  • Tetras
  • Otocinclus Catfishes
  • Platies
  • Plecos
  • Rasboras
  • Swordtails

Solution #2:

If you still insist on keeping Guppies with aggressive fish, then you need to provide a lot of hiding spaces. Thus, you need to add a lot of plants, drift wood and/or rocks to give both Guppy adults and fry someplace to hide in case they are being hunted and/or picked on.

Reason #5: Ammonia, Nitrite and Nitrate Spikes

If your Guppies are dying one after another, or seemingly overnight, then you may be experiencing sudden spikes to ammonia and nitrites in addition to prolonged exposure to a high nitrate concentration. These scenarios can occur when you overfeed your fish, forgot to quickly remove a dead fish, kill off a big portion of your beneficial bacteria as well as other factors.


If you suspect that you have a water quality issue, the first step we recommend taking is to test your tank water for ammonia, nitrite and nitrate. Ideally, you should keep you tank water to 0 ppm of ammonia, 0 ppm of nitrite and less than less than 40 ppm of nitrate. If you don’t have a test kit on hand, then we suggest getting the API Freshwater Master Test Kit, which you can find on Amazon.

If you find that any, or all, of the ammonia, nitrite and nitrate are above the aforementioned recommended safe zones, then you should do a 25% water change. We also recommend dosing Seachem Prime as it will detoxify ammonia and nitrite for a short period of time. The same chemical will also remove chlorine and chloramine, both of which will harm your fish and beneficial bacteria, from your tap water.

If you don’t have Seachem Prime already, you can purchase a bottle with this link on Amazon.

We suggest testing the tank water again 24 hours after the water change. If the ammonia, nitrite and/or nitrate levels are still too high, you should do another 25% water change (don’t forget to add in Prime as well) and then test again. Continue doing the same process over and over again until you bring down the ammonia, nitrite and nitrate concentrations to be safe for your Guppies.

To speed up the process, we recommend getting live beneficial bacteria product, like the Seachem Stability on Amazon, that will quickly get rid of ammonia and nitrite. Although there is no faster way to remove nitrates, you can add live plants (such as the aforementioned Hornwort and Java Moss) to your fish tank to help reduce the nitrate concentration in the long run.

For more in-depth tutorials to ammonia, nitrite and nitrate spikes, you can check out our following guides:

Reason #6: Low pH

Like other live bearing fish species, Guppies do not do well at all in acidic waters (which is below 7.0 in pH). The problem is that, even if you start off with neutral (7.0 pH) or slightly alkaline (above 7.0 pH) in the aquarium, the water will become more acidic over time due to the organic wastes being produced by your pet fish.


To prevent your tank water from becoming too acidic, and therefore potentially harming your Guppies, we recommend adding crushed corals. The corals will dissolve in acidic waters, which will then increase the pH and keep it stabilize.

If you are interested in using crushed corals, we recommend getting the CraibSea Aragonite, which you can find on Amazon.

Crushed corals are the safest way to increase pH as the other methods may cause drastic swings, which could also hurt your Guppies. With that sad, the other methods will also work if you take the necessary precautions. To find out more about the alternative ways to raise pH in your aquarium, you can check out this guide.

Reason #7: Suboptimal Water Temperatures

Your Guppies can also become sick if you are keeping them in suboptimal temperatures. Although this species can tolerate a wide range, which is between 64 to 82 Fahrenheit (or 18 to 28 Celsius), they tend to be healthier at around 70 to 78 Fahrenheit (or 21 to 26 Celsius).

Colder temperatures will expose the Guppy to potentially deadly diseases. A higher temperature will also increase their metabolism and decrease the amount of oxygen available in the aquarium, both of these will elements will shorten their life spans by making them burn more energy.


The solution is easy in this case. If your water is colder than 70 degrees, we recommend getting a heater. If you are concern that your tank may get too hot for your guppies, then you might want to consider getting a chiller such as the JBJ Aquarium Arctica Titanium Chiller.

Reason #8: Not Being Able To Acclimate

If you see dead Guppies shortly after adding them to your tank, then you could be doing something wrong during acclimation. If the water from the bag and your aquarium at significantly different, then you could risk stressing your new fish or even send them into shock, which may lead them passing away shortly afterward.

Another problem when it comes to Guppies is that they may never be fully acclimated to your water parameters. Even if you keep the water pristine and disease free, the fish may not live as long in your aquarium as opposed to where they were born.


To properly acclimate guppies, you first float the fish bag on your tank for around 30 minutes. Doing so will match the temperature of the water inside of the bag to your aquarium.

For the next step, we suggest testing the pH for both the water in the bag as well as your aquarium. If the difference is 0.2 or less, you can net the fish out of the bag and put it in your tank right away. If there is a bigger difference, then we recommend slowly adding water from your tank to the water in the bag until it is around 25% of the bag water and 75% off your tank water.

If you need more guidance, you can check out our acclimation guide for how to safely introduce new fish such as Guppies to your aquarium.

When it comes to long term acclimation, you should do your best to keep your tank water pristine even if your fish will never feel comfortable. The good news is that, if you are breeding Guppies, the new generation will be more acclimated to your water parameters, according to a scientific study on Poecilia Reticulata.

According to the research, it usually takes three generations for Guppies to be fully acclimated to their environments. So, if you can keep your Guppy colony alive, healthy and breeding for around a year, you have a pretty good chance at breeding Guppies that are fully acclimated to your tank water.

Reason #9: Guppy Diseases

As we stated previously, Guppies are regularly inbred, which makes the spawn weaker genetically and more prone to diseases. There is also a chance that your fish was bred and/or raise in a overcrowded small tank. In that setting, contagious diseases can travel quickly.

Even if the fish look healthy at the fish store, in the bag or even in your tank, doesn’t mean that your pet is completely disease free and won’t infect the tank mates later on.

Solution #1:

The best way to cure Guppy diseases is prevention. As we stated above, you first have to make sure that you buy your Guppies from a reputable seller that can produce strong genetics. By having a strong immune system from great genes, your fish have a better chance at fighting off parasites and infections.

As we mentioned above, you should also keep your water quality pristine for Guppies. This means having 0 ppm of ammonia, 0 ppm of nitrites, less than 40 ppm of nitrates, pH of at least 7.0 in addition to a temperature range between 72 and 82 Fahrenheit (or 22 to 28 Celsius).

Solution #2:

If you are planning to get new Guppies, then you should put them under quarantine by first placing them in another tank separated from the rest of the fish community you are planning to add them to. Even if your fish appear to be healthy, we still recommend medicating them as a precaution as they could still carry parasites that may manifest later on and infect the other fish in your main tank.

When it comes to medications, we recommend following Aquarium Co-Op’s method. To do so, you should add Fritz Paracleanse (you can also use API General Cure, which has the same ingredients, as an alternative) Ich-X and Mardel Maracyn 2. You should also use the same products on fish that are actively sick as well. With this combination, you should be able to get rid of most of the bacterial infections, fungal infections, internal parasites and external parasites that affect Guppies. You can see what each medicine treats below.

Mardel Maracyn 2:

  • Dropsy
  • Fin Rot
  • Gill Disease
  • Internal Infections
  • Secondary Infections
  • Septicemia
  • Tail Rot
  • Popeye


  • Cryptocaryonaisis
  • Ich
  • Saprolegniasis
  • Trichodiniasis
  • Velvet

API General Cure:

  • Gill Flukes
  • Hole-in-the-Head
  • Skin Flukes
  • Swollen Abdomen
  • Wasting Disease

You can use all three medicines at the same time. Just make sure you are using the correct dosage for your tank size. For more details on medicating your fish, you can check out the following Aquarium Co-Op video:


If you have a hard time keeping your Guppies alive, you can try the following:

  • Make sure you buy Guppies from a reputable seller, preferably one that use the line-breeding technique.
  • We also recommend breeding your own Guppies instead of keeping an all-male or all-female tank. This is because the offspring will be better acclimated to your tank waters. Not to mention that you can also create stronger genetics.
  • If you decide to breed, we recommend getting a ratio of at least two females for every male. Otherwise, the males may harass the females to death.
  • If you decide to breed, we recommend having a lot of live plants and other places for the newly born fry to hide as they may get eaten by the adult-size fish. Alternatively, you can move the babies into a separate tank and let them grow out.
  • If you decide to breed, we recommend adding a new Guppy to your colony every year to keep the genetics diversified.
  • When adding new Guppies to your tank, make sure that they are acclimated to temperature and pH beforehand.
  • You should also quarantine new Guppies and medicate them with a combination Fritz Paracleanse (or API General Cure), Ich-X and Mardel Maracyn to prevent the onset, and potential spreading, of deadly diseases.
  • If you are keeping Guppies with other type of fish, make sure that they are living with other peaceful species of similar sizes so that they won’t get picked on, eaten or killed.
  • When it comes to water parameters, you should keep Guppies at a pH of at least 7.0 with a temperature range of 72 and 82 Fahrenheit (or 22 to 28 Celsius). You should have 0 ppm of ammonia, 0 ppm of nitrites and less than 40 ppm of nitrates in your tank water.