Why do My Guppies Keep Dying?

Guppies are live-bearer tropical fish. They are popular among aquarium owners due to their vibrant colors and peaceful nature. Guppies are very easy to keep fish and are great for beginners. Although they are very hardy, often guppies keeps dying for no obvious reason.

The main problem is that most beginners have no clue regarding how to keep guppy fish. Therefore, they often face the problem of guppies dying in their aquarium.

I’ve created this article to help beginners figure out why their guppies are keep dying and what to do about it. I’ve also wrote a complete guide on how to care for guppies, where I talk about the biggest challenges of keeping guppies.

Reasons why Guppies are Dying

I will now highlight the reasons of guppy fish dying in your aquarium.

1. Poor Water Quality

The most common reason for guppies dying in your aquarium is the poor water quality. With feeding your fish you actually pollute the water in your tank. Guppies produce waste (they poop and pee), which is polluting the water. Overtime the pollution can become so high, that the guppies will get intoxicated and will die.

The lack of oxygen in the water can also cause guppies to die. Putting too cold or too warm water in your aquarium will cause death to your guppy fish.

Tap water contains chlorine, which is deadly to guppy fish. Though using tap water for your fish tank is find, but need to be treated before adding it to your aquarium.

2. Non-Cycled Tank

So you just started you first aquarium and you added some guppies. After one week, all your guppies started to die and you have no idea why that is happening.

Well, you did not cycle your aquarium.

Before you add fish to your aquarium, you have to cycle it first. The cycling process will take 1-2 weeks, depending on the size of your tank:

  1. Setup your tank and put add tank water into it
  2. Add de-chlorinator – I use & recommend Seachem Prime
  3. Add nitryfing bacteria – I use & recommend the API Quick Start
  4. Wait about 1-2 weeks for the beneficial bacteria to colonize the entire tank

At this point you can perform a water test with the API Test Kit. You test for ammonia, nitrite and nitrate. Ammonia and nitrite should be at 0 ppm, while nitrate can be at maximum 20 ppm.

At this point you can add fish. One day after adding the fish, perform another test to see, if the bacteria can keep up with the nitrogen cycle. Keep monitoring the tank for at least one week.

3. Raising Ammonia Level

Ammonia level in the fish tank should always be at 0 ppm. That said, there should be no ammonia present in your aquarium. The nitryfing bacteria should turn ammonia right away into nitrites and then into nitrates. This is the nitrogen cycle, which I explained above.

  • Ammonia can be caused by multiple factors:
  • Uneaten fish food will decompose and will turn into ammonia
  • Dead fish which is not removed from the tank will decay and will increase ammonia level
  • Dirty filter can also be a huge source for ammonia
  • Dirty substrate can also cause ammonia problems

Ammonia is very harmful for your fish. High ammonia level usually results in instant fish death. If the fish do not die instantly, because you were able fix the ammonia problem, they will still get ammonia burns. Ammonia burns will also result in death, but at much slower rate.

4. Overfeeding

I love feeding my fish and watch them eat. I bet you also like feeding your fish. However, overfeeding is very dangerous.

You should feed your adult guppy fish once a day or once every other day.

Feeding too much food to your fish, can cause health issues; just like with humans.

Feeding too much can result in uneaten food. As stated above, uneaten food will pollute your aquarium and can be a huge source for raising ammonia level.

Do not feed your guppies only the amount they can eat in 30 seconds. Repeat the process few times, until you think they got enough food.

Check out my guppy feeding / food guide, where I share a magic homemade fish food receipt, that will boost guppy growth rate significantly.

5. Overcrowded Fish Tank

Guppies reproduce at a faster pace. In a single month, female guppy fish can give birth to 20-120 guppies. That is why; it is pretty common that even larger aquariums with guppies can get overcrowded within a few months.

This can lead to a problem of not just overcrowding but lower oxygen levels. The lower oxygen levels can prove to be fatal for the guppies. That is why it is always important to control the population of guppies.

You can either do so by shifting the fishes to a separate tank or introducing only male guppies to your aquarium. This will allow you to control the population to a certain extent.

6. Water Temperature

Guppies are tropical fish. They cannot survive in cold water.

Guppy fish prefer water temperature between 72-82 °F (22-28 °C ). Guppies can survive in water with temperature  as low as 64 °F (18 °C), but the chances of diseases are very high. I don’t recommend keeping guppies in water colder than 72 °F (22 °C).

Warmer water is also dangerous for guppies. As the water heats up, the oxygen level of the water lowers. In water with temperature over 82 °F (28 °C) the oxygen level can be very low and guppies can die due suffocation.

7. Poor Guppy Genetics

When you are populating your aquarium with guppies, you should always consider guppies from trusted sources.

Guppies you will buy in big pet stores are usually the lowest quality. Although they are colorful, they might have bad genetics, which can lead to early death.

I’ve experienced myself with guppies that I bought from big pet stores do not live for more than 6 months in my aquariums.

On the other hand, guppies which come from guppy breeders, can live up to 2-3 years. Sure, they cost more, but their genetics are very good and can also produce very healthy and beautiful offspring.

Some of the breeds which you can opt for are:

  • Metal guppies
  • Albino guppies
  • Moscow guppies
  • Cobra guppies
  • Grass tail guppies

8. Diseases & Parasites

Due to bad genetics and poor water quality guppies can get sick quicker. There are few guppy specific desires. However the most common diseases which guppies get are ick (white spots on their body), velvet (gold dust on their body), fin rot and flukes. These common guppy diseases can be treated with the Seachem ParaGuard medication.

Unfortunately there are diseases, which can to be treated. For instance guppy fish tuberculosis, which is caused by a bacteria called mycobacterium has no remedies. Guppies affected with this disease should be removed from the tank and destroyed to stop spreading to the other guppies.

You can read more about guppy diseases and illnesses in my other detailed article.

How to Keep Your Guppies Healthy?

In the next part I will highlight some of the things you can do to keep your guppies healthy and avoid them dying very early.

1. Proper Feeding

Feeding your guppies quality and a variety of food will definitely contribute to the life-span for your fish.

You can feed your guppy fish commercial food, but try to use food from well-known brands, such as Tetra.

You can feed flakes, veggie pellets, spirulina tablets, freeze-dried brine shrimp, tubifex or blood worms.

If you have the time and the willing, you can prepare food for your guppies at home. You can cultivate live food such as daphnia, brine shrimp or vinegar eels.

If you breed guppies for fun or for profit and try to raise guppy fry quickly, here you can read about my secret food recipe for guppies.

2. Regular Water Changes

Doing regular water changes is also a key factor when it comes to keep your guppy fish health.

By changing water in your tank you will remove the toxins that are harmful for your guppy fish.

You don’t have to do big water changes. I recommend changing 20-30% of water once a week.

Don’t be lazy and don’t skip on water changes if you want to extend the life of your fish and keep them healthy.

3. Regular Tank Maintenance

Depending on the size of the filter once or twice a month it necessary to clean it.

If you have a sponge filter, just rinse it in aquarium water. Do not clean it in tap water, because you will kill off beneficial bacteria.

Do the same with internal or external filter. Rinse the sponge and the biological filter media with aquarium water. Don’t expose them for too long to air and don’t let it to dry out, because you want to keep the colony of beneficial bacteria intact.

It is also good to vacuum the substrate of your tank at least once a month. If you can, do some minor vacuuming every time you do a water change. This will help removing a lot of mock, which is a huge source for ammonia.

Cleaning the glass of your fish tank is not necessary but for the looks, you should do it once a week.

4. Prevent or Combat Diseases Fast

The best way to combat diseases is to prevent them. However occasionally your fish can get sick.

It is important to start the treatment for that particular diseases as soon as you see any sign of problem. Early treatment can save your fish’s life.

If necessary, remove the sick guppy fish from the main tank and add to a quarantine tank.

Before adding new fish or plants into your already established, disease-free guppy aquarium, quarantine them. Keep your new plants or guppies for 2 weeks in a quarantine tank and if necessary treat them for parasites, just to be safe.

Wrapping it up

I really hope, that this article has helped you to stop your guppies from dying.

If you still have any question and can’t figure out why your guppy fish are keep dying, please leave a comment below or send me an email describing your tank setup. I will try to help as quickly as possible to save your beautiful guppy fish.

23 Responses

  1. Amanda R says:

    I feel like I’ve concluded that my water care is not adequate enough and I need to do better. Thanks for this awesome article. How many fish tanks do you keep?

  2. Noeline says:

    My guppys are swimming like they busy sinking cant stay up. Like there to heavy to swim. I have fresh plants in and bohama fine stone in the tank

  3. Joshua says:

    I’ve come here after losing a sapphire scissor tail Guppy for unknown reasons the rest of the guppies are energetic and fine but the one that’s died has confused me

    • avatar Fabian says:

      Sorry to hear that! Did this guppy look healthy? Water parameters are good? What about ammonia level?
      Monitor your other guppies for a few days and check water parameters. Ammonia can kill guppies without any prior sign.

  4. Cynthia Parker says:

    My water tests are perfect except hardness. Very hard.
    My guppies will do fine and then suddenly die after a day of shimmy or hanging at the top of the tank or bottom of the tank. I do a partial change every week. Our thermostat is set to go to 70 every night and maybe the heater isn’t keeping up? Is there a type of springwater I could buy here in Florida that would provide better water? Once I used Crystal springs water and the fish were all dead the next day.

    • avatar Fabian says:

      What is “very hard” water? Guppies will thrive in hard water (dGH: 8-12).
      Spring water may contain elements, which will harm your fish. To decrease water hardness, you can use RO/DI or distilled water.
      Guppies can tolerate lower temperatures (68 °F). Check your thermostat and also water parameters. Sudden deaths could be caused by raising ammonia level. Maybe your filter and water changes can’t keep up with the raising ammonia and nitrite levels.

  5. Jessica McClure says:

    My guppy’s are dying and I’ve noticed that they have bumps on there heads is that common? Thank you

    • avatar Fabian says:

      That is not common at all. Some disease causes bumps on their head. It is hard to say what is wrong with your guppies without seeing them. Could you send me an image using the contact form?


    My guppy fish is dying now. It only moves at the certain time and it moves once I touch it. What can I do to make it live happily as before

    • avatar Fabian says:

      First of all, test your water parameters. If the water is good, then it is likely some disease. Also note, that guppies like to live in swarms, so keeping only a single guppy is not recommended.

    • Sanjeevi says:

      I can see white dots or white surface only guppies. After a week also my 10 guppies died. May I know the reason please

      • avatar Fabian says:

        Your guppies are probably infected with ich / ick. This diseases is easy to cure, though you act fast. Check out my guide on guppy diseases to find out how to cure white spots on guppies.

  7. Lilah says:

    Thanks to your website I will hopefully keep my fish alive and well #love your website

  8. Maria says:

    Help! I recently set up a guppy tank to breed and currently have around 10 fry, all was going well. This morning I woke up and one of my male guppies were dead, was very shocked. I have done a 30% water change and everything seemed fine again. However now one of my females is staying in the corner of the tank and her colour is drastically fading away I’m scared I’m going to lose her too. I can’t check my water levels until tommorow when I go to my local pet shop . What should I do??

    • avatar Fabian says:

      Hi Maria. If this is a brand new setup and the tank is not cycled yet, probably there is a problem with water parameters. Ammonia and nitrite levels should be at 0ppm.
      You can do partial water changes, but it takes time for the aquarium to fully cycle. It takes at least 6 weeks for an aquarium to be considered cycled.
      If you do have ammonia problem, I highly recommend using Zeolite ( in your filter for few weeks. This will get rid of the ammonia. But you will need to remove it from the filter, because it will get depleted after about one month.

      • Maria says:

        The tank has been set up for months and is fully cycled. Just recently got the guppies I didn’t get a chance to get my water levels tested still and my female is still staying in the corners I’ll let you know my levels tommorow

  9. Amy says:

    Hi, I’ve lost another guppy. I had issues with my previous tank so upgraded to a slightly bigger one with a better filter. By this point I only had 1 guppy left so I got him 2 new friends. I had the new guys about a week. Everything was fine when I went to work then a couple hours later I get a message from my mum saying one had died. She checked the water and it was perfect. I also test for ammonia daily to be safe. My tanks are always cycled before introducing any fish to them. I cant work out why I keep having this issue. The other 2 guppies seem fine. I have 5 neons in the same tank which are also fine. I do have a bigger community tank which never has problems but due to the fish in that tank, I dont think it would be safe for guppies. The guppy Tank temp is at a steady 25c as I was advised this is a good temp for them. This is the only type of fish I seem to have issues with. Please help.

    • avatar Fabian says:

      Do you see any type of anomaly on your guppies? Red spots, stringy poop, or anything else?
      It is really hard to tell what is the problem with your guppies without seeing them.
      Ammonia is at 0ppm and water temperature at 25 °C are good values.
      How often you do water changes?

  10. Sam says:


    Just wondering if you could help me. I have the Fluval flex 57 litre tank and I keep losing guppies. I had 6 guppies and 10 neons and a lot of plants. I have lost 4 guppys now all at separate times over the last few months (I replaced one 2 weeks ago and he has died). I only have Males. I test my water every week at the local Aquarium (not a pet shop) and sometimes I’m a little low on KH but that’s it, all my levels are perfect. My water temp is always between 27-28 degrees Celsius. I have changed all my cleaning products to natural (and I cover the tank when cleaning the house as well).

    I have goldfish in another tank and they are thriving. I just don’t understand why they keep dropping off. They are all spaced apart when they die and they are fine one day and then gone the next 🙁

    • avatar Fabian says:

      It is really hard to tell why your guppies are dying, but I have few things I suspect.
      1. The filtration can’t keep up with the number of fish. – I had the same problem on a new setup. The filter I got with my aquarium was too small for the amount of fish I was keeping in it. Often ammonia spikes were damaging and killing my guppies. Try to measure ammonia level, one hour after feeding your fish.
      2. The water temperature is a bit high for your fish. At 28°C the oxygen level in the water starts to deplete. I suggest lowering the water temperature to 24 °C or add an air stone to the aquarium.
      3. Don’t know from where you are buying your guppies, but if they have bad genetics, it could also be a factor of sudden, unexpected death. I found that guppies which are sold by large super markets usually have a short lifespan.

      From what you wrote, I suppose your aquarium is already cycled and is running for at least 6 weeks. So this should not be a problem.

  11. Sherri L Michaud says:

    I have successfully bread guppies in the past but it has been years. I started a new tank 5 months ago (4 females, 2 males) in a 10 gallon with an African Dwarf frog. Every month or so I lose a fish and what is more odd is that they aren’t breeding. I’ve only had one batch of fry since January. The water tests fine, occasionally a little hard but no other issues. Temperature is at 78 Fahrenheit with an air stone and an Aqueon 10 gallon filter. They get fed once a day (I dont think they’re over fed as I’ve never had this issue with previous tanks) Why are they not breeding? Why are they dying? I dont know what else to try!? 🙁 All the decor was purchased at Petsmart so I dont think anything is toxic. I’ve never seen guppies not breed!?

    • avatar Fabian says:

      Hi Sherri. I don’t think you are doing anything wrong. The amount of fish you keep in a 10 gallon tank is OK. Usually guppies you purchase from Petsmart or other big stores do not live long. I’m not exactly sure why, but I experienced the same and many aquarists reported the same problem.
      In my opinion your guppies breed, however they might drop the fry, when you are not around. If you don’t have many hiding spaces, adult guppies will eat all the fry and you will not notice anything. I suggest you to take a photo of your female guppies often and watch their belly size. If their belly gets smaller, it means, they gave birth. Any you need to wait another month for a new batch of fry.
      If you want to save your fry, add live plants. Add Java moss or Guppy grass. These are easy plants and are perfect for fry to hide.

  12. malika says:

    Thank you ,for this article it is important ,good.

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