9 Reasons Guppies Die And How To Prevent It from Happening!

Last Updated on 2023-12-28

Ever wonder “why do guppies die?” Maybe your guppy seemed healthy one day, only for you to look into your tank the next and see they’d passed away. Or perhaps, you could see they were getting weaker and weaker before passing away.

Whatever the case, this article is going to explain all the reasons guppies die, and more importantly, the things you can do to prevent it for as long as possible!

Why Do Guppies Die?

There are a whole number of reasons that your guppy might die, but you can normally figure out what’s caused it, and in most cases, prevent it from happening in the first place.

These are all the reasons that your guppy may die, and more importantly, how to stop it from happening as well.

Poor Water Quality

Poor water quality is probably going to be one of the biggest reasons your guppy may die. After all, it’s essentially the equivalent of you trying to live somewhere the air is contaminated and full of things that want to kill you.

If the quality of your water is poor, then there’s going to be a build-up of ammonia, waste, bacteria, parasites, and fungus.

How To Keep The Water Quality Good

Fortunately, it’s not hard to keep keep great water quality in your tank for your guppies. The two best things you can do is make sure that you’re using a filter in your tank and that you’re changing the water regularly.

When there’s a filter in your tank it’s going to constantly, cycle the water. Removing a lot of the waste and debris that begins to build up, as well as ammonia.

(Find out more about why guppies need filters.)

However, a filter on its own isn’t enough. As well as using a filter in your tank, you should also be performing water changes regularly as well. The amount of water changes you’ll need to perform depends upon the size of the tank, as well as the amount of fish that are in it.

The smaller the tank, or the more fish, the more often the water will need to be changed.


Another big reason that your guppies may end up dying is when they’ve been overfed. You may not think this is going to be a problem, but it’s actually a fairly common reason that tropical fish dies.

Guppies are going to try and eat as much as they can, and this can often result in constipation which can then lead to swim bladder disease. Both of which can become fatal to guppies.

As well as this, if you’re feeding them lots of a certain food, they may also develop health issues that can kill them. For example, blood worms are quite fatty, and can often cause fatty deposits to build up in your guppies liver.

Another problem with overfeeding your guppies is that the excess waste is going to increase the ammonia in the tank, which is dangerous for your fish.

How To Stop Overfeeding Your Guppies

To stop overfeeding your guppies, you should know how much to feed them every day. As a rule of thumb, you should feed them for two minutes twice a day. You should sprinkle in a few flakes, and once those are all gone, sprinkle in some more.

Once the two minutes are up, stop feeding them flakes, and remove any flakes that may be sinking to the bottom.

This also applies to any other type of food you’re feeding them as well.

Also, don’t be afraid to fast your guppies for a couple of days every once in a while. This may sound cruel, but it’s actually good for them. It’s going to help clear their digestive tract and reduce the chance of constipation.

The Tank Is Overcrowded

If your tank is too overcrowded or too overstocked, then it’s going to increase the bioload, which isn’t good for your guppies.

One downside to guppies is that they’re livebearers. So even if you buy the right amount initially, if left alone, you could potentially have far too many in your tank if the babies grow to adulthood.

For some clarity on just how many guppies could end up in your tank. Each batch of fry typically contains between 20-120 guppies. Females also give birth about once a month. So 3-4 guppies can quickly turn into a lot more.

Not only is an overcrowded tank going to increase the bioload, but it’s also going to lower the oxygen levels in the tank, which can be fatal to fish.

How To Deal With An Overcrowded Tank

Obviously, the best way to deal with an overcrowded tank is to remove as many of the fish as you can. If possible, you can try moving fish to another tank, or try to give them away to pet stores or people.

If your guppies are having too many babies, you can also introduce fish to the tank that will happily eat them, such as angelfish.

Lastly, if it’s causing the oxygen in the water to be too low, try adding lots of plants and an air bubbler to help increase the oxygen levels.

Tank Mate Aggression

Now is all the time to look for aggressive tank mates. I’m not talking about fin nippers or other guppies showing aggression (although this can also be dangerous). But tank mates that are a lot bigger than them, or a lot more aggressive (think angelfish, gouramis etc)

How To Stop Tank Mate Agression

Honestly, tank mate aggression is really hard to stop. Oftentimes the best thing you can do is simply move your fish to another tank. In times when this isn’t possible, you should try to add as many plants as possible to help break lines of sight and give your guppies places they can be safe.

It’s Too Hot Or Cold

If you’ve been keeping your tank too hot or too cold for too long, then it could be the reason that your guppy has died. Ideally, guppies need to be kept in temperatures between 74-82°F.

When the water is too cold, your guppy’s metabolism will slow down. Which results in lethargy, lack of appetite, an increased risk of constipation, and a weakened immune system.

And when the temperature is too hot, then they’re going to be far too energetic. This may sound good but it actually puts massive amounts of stress on their body, which will weaken their immune system as well.

Not only this, but in warmer water, the oxygen levels lower. This could mean that your guppies will die of suffocation.

How To Make Sure The Temperature Is Perfect

To make sure you’re keeping the temperature in your tank consistently perfect, you should be using a heater as well as a thermometer, so you can keep an eye on it.

Even if you live in a country where the temperature is always hot, you should still have a heater. Oftentimes at night the temperature can drop massively, as well as on windy days.

If your tank is getting too hot, you can buy a fan that blows over the aquarium and helps keep it cold. You can also try removing some water and replacing it with cold water to help cool down the tank. (Just make sure you’re not replacing too much water at once.)

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Disease And Illness

And of course, another reason that your guppy may have died is due to a disease or illness. Fortunately, in most cases, you should be able to see the signs of disease, and treat your guppy when neccesasry.

Diseases are either going to be caused by bacteria, parasites or fungus and knowing which disease your guppy has will help reduce the spread to other fish in your tank.

Some of the most common diseases you can see in your tank include fin rot, velvet, swim bladder disease, ich, and dropsy.

And while it’s not a disease, if left untreated, constipation can also kill your guppies as well.

How To Deal With Disease And Illnesses

There are two ways that you can deal with disease and illnesses. The first way is to prevent them from happening in the first place, and the second way is treating them.

To prevent disease from happening, you should make sure that you’re feeding your guppies high quality food, the water is in good condition, and that you’re removing any other fish that are diseased or ill.

To treat the disease or illness, you’ll first need to diagnose what’s wrong with them, before administering the treatment that they need.

In some cases though, especially in older or weaker guppies, when they do suffer from a serious disease, it’s a death sentence.


There’s no doubt that when a fish is becoming pregnant over and over again, it’s going to take a massive toll on their body. Every time that your female guppy gives birth, it’s damaging their body, and this, of course, is going to weaken them.

How To Deal With Pregnancy

Unfortunately, there’s not a lot you can do for this one, shy of not adding any male guppies into your tank. Even with one male guppy in the tank, most of the females are going to get pregnant.

Poor Genetics

Poor genetics can also be to blame for your guppies untimely death. This is most common when they’ve been brought from places who care about profit over the health of their fish.

How To Deal With Poor Genetics

If you’ve already bought guppies there’s not much you can do about poor genetics. However, in the future you can go to trustworthy breeders.

Generally speaking, big brand stores, don’t have the best interest of you or your guppies in mind, they’re just trying to turn over a profit. Instead, you should be going to local fish stores, who are well known and who take care of their animals.

pH Fluctuations

While guppies can generally adapt to any pH in their tank (within reason) if the pH is fluctuating a lot it will stress them out, and can even kill them. This is why it’s so important to make sure the pH in your tank isn’t fluctuating.

How To Stop pH Fluctuations

If the pH in your tank is fluctuating, it’s most likely happening when you’re adding new water to the tank. The best way to stop this from happening, is by using a pH buffer like pH up and pH down. Make sure to do this before adding it to the tank, so it’s the perfect pH as it’s going in!

Why Do Guppies Die Suddenly?

Sometimes there seems to be nothing wrong with your guppy, but they drop dead overnight. This can be even more confusing. As you may have no idea what’s caused it.

However, here are some of the most common reasons that guppies die suddenly.

Temperature Shock

While you already know that maintaining the right temperature for your guppies is important. If the temperature drops too quickly it can kill them straight away. Even if the drop stays within the temperature range they can normally survive in.

A drop of 2-3°F in the temperature in a couple of hours is more than enough to kill a guppy or the whole school.

So if you notice that your guppy has died suddenly check the temperature of the tank.

How Do You Stop Temperature Shock

The only way you’re going to be able to stop temperature shock is by investing in a high-quality heater. One that you know isn’t going to break. Doing this is vital, and luckily, a high-quality heater in a small tank isn’t going to cost you that much at all.

(If you’re not sure what heater to get then the Fluval M Series are a great choice!)

New Tank Syndrome

Another common reason that your guppy may have died is something called new tank syndrome. This is when you add them to a tank which hasn’t fully cycled yet. If it hasn’t fully cycled then there won’t be any bacteria in the tank to deal with the bioload.

And because of this your guppy may end up succumbing to ammonia poisoning.

How To Deal With New Tank Syndrome

Fortunately, there are ways to deal with new tank syndrome. The best thing you can do is wait 5-6 weeks for the tank to cycle fully, without adding any fish to the tank.

However, if it’s already too late for that, then the second option is to perform water changes every day to keep the ammonia levels in the tank low. As well as that you can also add an ammonia detoxifier which is going to render ammonia harmless to your guppies, while still leaving it in the tank to feed good bacteria.

Ammonia Poisoning

A build up of ammonia can happen rapidly, if you’re not taking sufficient care of your tank. And when it does it’s not uncommon for guppies in your tank to succumb to it fast.

So if you do notice that one of your guppies has died, the first thing you’re going to want to do is check the water parameters to make sure there hasn’t been a build up of ammonia.

How Do You Prevent Ammonia Poisoning?

Preventing ammonia poisoning from happening isn’t difficult. In fact, if you’re taking care of your tank then it shouldn’t happen in the first place.

To prevent ammonia poisoning from happening, make sure you have a filter in your tank, you’re performing regular water changes, you haven’t overstocked your tank, and that you’re vacuuming the gravel and removing waste regularly.

And of course, make sure you’re testing your water parameters to make sure everything is in check. If you’re not sure what to use to test your water parameters, then I highly recommend the API Master Test Kit.

Chemicals Have Entered The Tank

Another extremely common reason that your guppy may have died suddenly is when chemicals have entered the tank that shouldn’t have gotten in there. If you’ve forgotten to add water conditioner to water in your tank then this will poison your fish.

However, it’s not just that. any chemical such as deodorant that has entered your tanks water could prove to be fatal to your guppies.

How To Stop Chemicals Killing Your Guppies

Fortunately, there are a few ways you can stop chemicals from killing your guppies. The first, is to use a water conditioner whenever you add new water to the tank to remove any chlorine and chloramine.

Secondly, put a lid on your tank so that it’s much less likely for airborne chemicals to get into the water.

And lastly, make sure you have chemical filter media to remove any chemicals that do make their way into your tank.

How Long Do Guppies Live?

Guppies aren’t the longest living fish. Generally, in good conditions you can expect your guppies to live for around 2-3 years. So if your guppy has died, you can’t rule out old age. As you may have got it when it was a year old from the shop


Now you know all the reasons that your guppy may have died suddenly. And more importantly you should be aware that most of them are preventable as well!

If you liked this article make sure you check out the rest of the website! Otherwise have a great day!

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