How to Treat Sick Guppy Fish? Diseases, Parasites & Illnesses

Keeping a pet, especially as a kid, is a great experience that helps you grow up. Having to take care of an animal’s needs requires attention, patience, and careful thought. If you’re like me, then you’ve had a pet when you were a kid. I had a few guppies that my parents bought for me.

Those small, feeble-looking and brightly colored fish made my childhood better. But at some point, they got sick and I didn’t know what to do, so I lost them.

Now, I’m here writing about guppy diseases and potential treatments, hoping to save you the grief I went through back then. At first glance, guppies look as if they could die from anything but that’s not entirely true. They’re quite resilient but certain diseases get the better of them.

In the following paragraphs, I’ll outline the most common guppy diseases, how to identify them, and how to offer immediate treatment.

Common Guppy Diseases & Treatments

Before we start, I should provide a couple of tips for preventing most guppy diseases. Throughout the years, I’ve tested and experimented with these methods, and they worked wonders. Here’s what you can do to prevent guppies from falling ill:

  • Don’t underfeed or overfeed your fish
  • Always maintain temperature and water levels at optimal parameters
  • Visually inspect your guppies daily
  • Change the water in the tank weekly, and clean the tank thoroughly
  • Immediately remove any dead or sick fish from the main tank
  • When buying a new guppy, quarantine the fish in a backup tank for 3-4 weeks. If it doesn’t show signs of illness, you can put it with the others

But despite these countermeasures, your guppies may still fall ill. In this case, you’ll want to quickly identify the cause of the problem and deal with it. Depending on the symptoms, your guppies may suffer from a wide number of diseases. Below, I’ll go into more details on these illnesses!

Before that, let me say that stress is one of the most common problems guppies deal with. It’s also the number one cause of most diseases. That’s because stress makes the guppy vulnerable to infections and parasites by weakening its immune system. But what could guppies be stressed about? Is the water not clean enough? Are other guppies bullying it?

Well, stress generally comes from a lack of safety. In their natural habitats, guppies live among leaves, branches, plants, roots, and reefs that they can hide inside. To offer that sense of safety, add such decorations to the tank. Plenty of hiding places will also put your guppies at ease.

Guppies may also feel stressed because of an over-crowded tank, inadequate temperature in the tank, or the presence of other fish varieties in the tank. Lastly, the quality of the water in the tank can heavily stress your guppies. That’s why I recommend partially changing the water in the tank weekly.

Now, let’s move on to the main dish – common guppy diseases and treatments!

Ich – White Spots

Ich is a very common guppy disease that manifests through white dots appearing on your fish. It looks a bit like mold if you think about it. These white spots are actually a parasite with an unpronounceable name (Ichthyophthirius multifilis) that means “fish louse with many children.” You’ll notice your guppies scratching against the rocks, losing appetite, and forming white spots on their skin.

That’s a clear sign of the Ich or Ick disease. The parasite has entered their system and is currently spreading and eating the fish’s blood and dead epithelial cells. The white spots are actually the result of the parasite burrowing into the skin. For your peace of mind, the fish only feels a mosquito bite when the parasite burrows into it. The fish will want to scratch this “itch” by rubbing itself against rocks and other hard surfaces.

Fortunately, it’s very easy to treat Ich. Just do this:

  • Gradually raise the water temperature to 80 degrees Fahrenheit (26.6 Celsius)
  • Use Seachem ParaGuard in a recommended dose
  • Alternatively, add 1 teaspoon of aquarium salt per gallon of water
  • Do nothing else for 4-7 days
  • Start decreasing the water temperature to normal
  • Change about 70% of the water in the tank, making sure you thoroughly clean the substrate

This should kill off the parasites and get you rid of them. However, if left untreated, Ich will eventually start dividing into hundreds of other parasites. When the main parasite gets its fill of sustenance, it sinks to the bottom of the tank, creates a membrane around it, and starts dividing. The newly-created parasites called tomites will start looking for fresh prey.

The medication only works during the free-swimming stage when the parasite still hasn’t burrowed into another fish. This period only lasts 3 days, so apply the medication in that timeframe to save your guppies! By raising the temperature, you essentially shorten the time before the parasite leaves a fish and becomes vulnerable to medication.

Velvet (Oodinium)

Yet another parasite that likes dining on fish, Oodinium is the cause for the Velvet disease. As cool as the name sounds, what happens to the fish is not pretty at all. After attaching to a fish, the parasite will start feeding on it, absorbing the nutrients until it grows big enough. Then, it’ll leave the fish and start dividing, creating hundreds of new parasites that have 24 hours to find a new host or perish.

Velvet manifests through golden dots and spots that look a lot like rust. These dots are much finer and less visible than Ich, so it may be hard to see them. But if your fish suddenly losses its appetite, becomes lethargic, and starts having rapid breathing, Velvet may be to blame. The guppy will also start scratching itself against rocks and other hard surfaces, trying to get rid of the parasite.

Due to its nature, Velvet only becomes apparent during advanced stages when the fish isn’t feeling too well. At that point, you need to start the treatment immediately to save your fish. Like before, the treatment will only affect the parasite when it leaves the fish. When inside the fish, Oodinium is impervious to any chemicals in the water.

This is the treatment:

  • Raise the water temperature
  • Turn off the lights in the aquarium for a couple of days
  • Add aquarium salt
  • Copper-based medication is ideal, like Seachem Cupramin
  • Stop carbon-filtrating the tank

Copper is the most efficient treatment for Velvet disease in guppies. But if you don’t have access to copper, Atabrine works as well. Light is also an important factor in eradicating Oodinium parasites. After increasing the temperature to 82 degrees Fahrenheit, the lifecycle of the parasite will quicken. It will be forced to leave its host shortly, and then the medicine will kill it off.

If you use copper, you won’t be able to wash it out from the tank. It’ll also be impossible to keep any shrimps or snails in the tank because copper is deadly to them. But the Velvet disease is gone at least!

Fin And Tail Rot

Fin and tail rot is a very common disease among guppies. It often appears due to the stress of overcrowding, poor water quality, ammonia burns, or infighting. If you recently moved your fish to a new aquarium or if there are too many fish inside, they may become stressed.  This will cause their fins and tail to rot, a condition that initially manifests through discoloration of the fins.

If left untreated, parts of the fins will begin to fall off alongside dead flesh. Bloody patches will be present on the fins, and more tissue will fall off. Fungal infections can also lead to the so-called fin and tail rot. But that’s not the only possibility. Bacteria are another potential cause of fin rot.

A rule of thumb is to look for visible damage on the fins. If the fins look damaged and the rot has started to set in, then it’s most likely a fungus. If the rot is there but there’s no sign of visible damage, then bacteria is to blame. To properly treat fin and tail rot, do the following:

  • Isolate the sick fish to another tank
  • For bacterial infections, use antibiotics like Seachem ParaGuard, Maracyn, Tetracycline, or Maracyn 2
  • For fungal infections, use special medication
  • If the cause for the fin rot is an ammonia burn, switch to a higher-quality water

I recommend listening to your veterinarian at all times. Antibiotics and special medical for fin and tail rot have different instructions that may vary. Maintain the treatment for as long as the veterinarian recommends. Cutting it short may lead to a reappearance of the rot. Some fish species may also benefit from aquarium salt but others find it disagreeable and uncomfortable.

Usually, the temperature and the pH of the water is a crucial factor for the appearance of fin and tail rot. So, make sure the water is optimal, and that it doesn’t contain any ammonia, chlorine, or nitrites in it. The nitrate level should also be below 40 ppm (mlg/L).

Guppy Disease (Protozoan)

Protozoan is a common disease for fish, especially guppies. They’re the most prone to becoming infected with this parasite. After it attaches itself to the fish’s skin, the Protozoan infests its host through the muscles and then enters the bloodstream. There, it’ll start feeding with blood and other local tissue until it becomes satiated. Eventually, the Protozoan will detach itself from the fish, drop to the base of the aquarium, and enter a reproductive phase.

As usual, look for signs of lethargy, lack of appetite, ragged breath, and an overall weird behavior from your guppies. When the parasite infects the host, it’ll feed on most essential nutrients, weakening the fish’s immune system. The fish may also appear discolored or grow different colorations on its scales. An unheated tank or bad quality water are the likeliest causes for Protozoan infection among guppies.

To prevent this, I recommend keeping the water at a stable temperature and adding a heater. Also, change the water regularly with fresh, unchlorinated, and nitrite-free water that contains no ammonium. When this disease hits, you can do the following:

  • Use Formalin or Malachite Green to treat Protozoan in its early phase
  • Seachem Cupramine is ideal for more advanced phases of infection
  • After you complete the treatment, change 50-70% of the water in the tank

That’s about it with Protozoan!

Mouth Fungus & Columnaris

Columnaris may look like a fungus but it’s a bacterial infection, in fact. The name comes from the columnar-shaped bacteria that inhabit all aquariums. When it infects a fish, the symptoms revolve around white and grayish spots on the head or around the fins and gills. These lesions will look pale at first but as the disease advances, they will become yellow or even brown.

The lesions on the back of the fish will run parallel on the sides, creating the shape of a saddle, hence the name of “saddle-back” given to this disease. As for lesions in the mouth, they will appear cottony or moldy. As the disease progresses, it’ll eat away the mouth of the fish, erode the fins, and affect the gills as well. The fish may start gasping for breath or having a ragged breath because of this.

Again, the likeliest cause for infection with Columnaris is stress, which can come from bad water, overcrowding, and more. This infection is viral and highly contagious, to a point where the fish can get it from containers, food, nets, and so on. That’s why I always recommend you use sterilized equipment when cleaning the tank or handling the fish. You never know what infection you’re carrying.

Columnaris is especially deadly and, if left untreated, it can wipe out the entire fish colony in a tank. When the first symptoms appear, don’t hesitate to begin the treatment. To treat Columnaris, follow the steps below:

  • Use Formalin and Maracyn to fight against the bacterial infection
  • Perform a 50% water change, add one teaspoon of salt per gallon of water every 3 days, and then wait until the infection disappears. Finally, do another 50-70% water change
  • You can do a 30-minute potassium permanganate bath but never go above the 10mg/l quantity of potassium permanganate. It can burn your fish badly due to its oxidizing properties

If you take good care of the fish, then you’ll most likely prevent Columnaris and mouth fungus from appearing.


Dropsy is the type of bacterial infection that rapidly kills its host if not taken care of. It infects the kidney or liver and bloats the abdomen with liquid. The swollen fish becomes discolored and its scales may become elevated, looking like pine cones. Guppies may even have problems swimming because of how bloated they are. Usually, dropsy appears because of stress or overfeeding with blood worms.

Unfortunately, Dropsy is one of the untreatable fish diseases. Once it has taken hold of the fish, it’s a point of no return. The internal organs of the fish will be damaged beyond repair. However, if dropsy didn’t cause the swollen belly, then there are chances to save the fish. Feed the fish good food, make sure the water parameters are optimal, and take good care of the fish.

From personal experience, I can tell you that Epsom salt can slow down the progression of dropsy. It’ll also take away the pains and help the guppies relax. It won’t cure the sickness, though. Just put 2 tablespoons of Epsom salt in one gallon of water, and put the fish in it for 30-45 minutes. Don’t put the salt in the main tank because it won’t be as efficient anymore. But make sure the water in the separate container has the same temperature like the one in the aquarium.

Gasping And Swollen Gills

Swollen gills are often caused by ammonia in the water or carbonate poisoning. Ammonia occurs naturally from decomposing organic matter, fish food, and fish waste. As for carbonate, it’s found in the substrate and in the rocks. Ammonia can burn the gills of fish, while carbonate is quite deadly in high quantities. Guppies use their rake to extract oxygen from the water, but if the water is polluted, the gills and the rake are affected.

When the gills are swollen, fish won’t be able to breathe properly. So, you’ll often see them gasping for air at the surface of the water. To treat swollen gills, you should:

  • Perform a 50% water change if the guppies are gasping for air and if they move their gills frantically
  • Test for ammonia in the water and oversee the water parameters over the following days
  • Stop feeding your guppies. Feeding them will lead to higher intakes of ammonia
  • Add nitrifying bacteria into the water

This should solve the problem immediately. If not, contact a veterinarian for extra assistance.

Red Blood Spots

Again, ammonia and nitrite poisoning can lead to red blood spots on the body and stomach of the guppies. From personal experience, I’ve noticed that new aquariums bear the maximum risks of nitrite and ammonia poisoning. It takes about 6 weeks for a new aquarium to be fully cycled. Until then, the risks are still there. When introducing new fish into an aquarium, the nitrite and ammonia levels will go up.

That’s because there are insufficient beneficial bacteria to transform the ammonia and nitrites into nitrates. Basically, the aquarium needs to be used before it can safely house fish. But to be used, you have to house fish in them. Quite the conundrum, right? Well, the world won’t implode because of this paradox, thankfully. The truth is that both ammonia and nitrites are invisible killers that barely leave a mark.

Red blood spots on the stomach and body are one of these signs. There’s no way to treat the red blood spots, though. However, you can save the fish if it hasn’t been poisoned too strongly. You should rather avoid ammonia and nitrite poisoning rather than trying to treat them.

To do this, simply let the aquarium sit still for about 6 weeks before putting fish in it. Use a test kit to measure nitrite, ammonia, and nitrate levels in the aquarium. You should also change the water frequently, more than once a week if the aquarium is new. I personally use Seachem Ammonia Alert to measure the ammonia level in my aquariums.

Viral Hemorrhagic Septicaemia (VHS)

It’s hard to detect this disease because it mainly affects the blood of guppies. When you start seeing lesions and sores around the body, or when the fins start rotting, it may be VHS acting up. It’s a virus that affects the blood, makes fish lose their appetite, and get a darker color. They may also have bulging eyes and pale gills – all the symptoms of something wrong. So, when you notice any of these things, treat your fish with Maracyn 2, API Furan 2, or other antibiotics.

I also recommend doing water changes after you finish with the treatment. Fish can have huge health problems if the water level isn’t optimal. Plus, you need to get rid of excess medicine in the water after the fish are healthy again. Those antibiotics can harm them long-term if they remain in the water.

Popped Eyes

Fish can get popped eyes not because they’re very surprised but rather that they’re sick. Many things can lead to this condition, and it’s quite difficult to diagnose it accurately. A veterinarian can narrow it down among many factors, including bad water quality, tuberculosis, infections, dropsy, fungal infections, and more. While it won’t kill the fish, this condition can cause blindness, which isn’t a fun idea for anyone.

I’ve got no good advice on this front. I highly recommend you consult a veterinarian and see what he has to say. While it’s difficult to narrow down the cause, perhaps the veterinarian will know what’s up.

Swim Bladder Disorder

Guppies use their swim bladder to maintain a steady balance while swimming. It also controls their buoyancy. But what happens when this essential organ gets sick? Well, this disorder is not very common and, in most cases, stress causes it. When you move the fish to another tank, it might become stressed. When you see the guppy floating upside down or angled, seemingly out of balance, the problem becomes clear.

If the water is very rich in ammonia or other chemicals, it may result in swim bladder inflammation, as well. One clear symptom of this is when the fish starts floating head-down, heading toward the substrate and standing on its head. This type of inflammation occurs due to a virus and, at present, it has no cure. I recommend isolating the sick fish from the main tank so it doesn’t get others sick, as well.

Gill Worms and Flukes

Did you ever see tiny white worms on your guppies? They are some mean bastards that can make the gills start bleeding. When this happens, fish will often start gasping for air at the bottom of the aquarium or struggle to breathe on the water surface. These worms appear when you bring new fish or plants to the aquarium. Add bad water quality to the equation and the gill worms can spread even faster.

To treat gill flukes, you should use medicine to treat the entire aquarium. If you notice these worms in the beginning stages of infection, then you can save the fish by following the medication instructions. But if their gills have already started bleeding, they’re as good as dead, unfortunately.

Camallanus Internal Worm

Butt worms, that’s what Camallanus Internal Worms are. They’re some of the most common worms for guppy fish. You’ll see them dangling from the butt of your guppies, measuring about 0.8 inches in length (2cm). This worm is either brown or orange, so it won’t be hard to distinguish it from the fish waste. It’ll also be squiggling like the worm he is, the bastard.

At times, other fish will even attack this worm coming out of the but of another fish. So, if you see your guppies ramming each other in the butts, this may be the problem. Their origin is a mystery but I theorize they come from fish kept in external ponds that are fed with live Cyclops. To get rid of this worm, do this:

  • Use Levamisole (also known as Ergamisole) for 5 days. Alternatively, use Parcide X, D, or Fenbendazole
  • Vacuum the substrate and clean the filter afterward
  • Perform a water change of 70-90%
  • Rinse and repeat after 3 weeks

This should get you rid of the nasty butt worms. But make sure you don’t feed your fish live Cyclops!


Another Protozoan parasite is ravaging your fish population. This one is very rare and you may never deal with it. But it’s worth knowing about. Overall symptoms of the Hexamitia parasite include white and stringy feces, pale skin color, loss of appetite, and holes in the head of the fish. Lesions may also appear on their bodies. This parasite generally appears in overcrowded aquariums with a bad water filtration system. If you don’t change the water frequently enough, it may also lead to an infection with Hexamitia.

To treat this parasitical infection, do this:

  • Use metronidazole (also known as Flagyl) and medicate the fish food
  • If the fish has no appetite, medicate the water (250mg of medicine per 10 gallons, once a day, for 3 days at least

You may need a veterinarian prescription to buy metronidazole, though. In any case, I highly recommend you consult a veterinarian if you think your fish have Hexamitiasis.

Bent Spine

Also known as scoliosis, Bent Spine occurs due to inbreeding among fish. This is mostly a genetic disorder that you can’t cure or treat. Though it’s not contagious and it can’t spread to other fish. Unless you reproduce the fish with scoliosis, that is. You can check for scoliosis by looking at the fish from above or from the sides. This condition manifests through swimming problems, a lower lifespan, and slower growth.

Fish Tuberculosis

This is the only guppy disease that’s transmissible to humans. I recommend extreme caution when handling sick fish. A bacteria called mycobacterium causes tuberculosis, and the sickness manifests through:

  • Loss of appetite
  • Hollow-belly
  • Ulcer on the body and anus
  • Skin discoloration
  • Tail and fin rot
  • Inactivity

Tuberculosis is inheritable and contagious if other fish eat the dead one. So, I recommend immediately isolating the sick fish in a quarantine tank. If other fish have tuberculosis symptoms, treat them with Kanamycin, Neomycin, and Isoniazid antibiotics. If their health doesn’t improve, I recommend euthanizing the sick fish so they don’t infect the others.

How To Treat Your Fish Tank with Medication?

When providing medication to your fish, I highly recommend reading the instructions first. Make sure you don’t overdose on the medication, even if you want to get rid of the problems faster. An overdose may harm your fish even worse. As the saying goes, a poison can become a medicine in low enough doses, but the opposite is also true.

Moreover, before applying the medication, take away the activated carbon media from the tank. It can interfere with the medication and render it ineffective. After using the medication and dealing with the parasites, you can put it back. But make a big water change after providing the medication so you eliminate the remainder of the medication.

Usually, a fish veterinarian should be able to help with medical advice and medication recommendations!


I can’t overstate the importance of good-quality water and a low-stress atmosphere for the fish. Guppies can easily become sick because of stress and bad living conditions. Change the water regularly, clean the tank, and try not to move the fish to another tank too often. Feed them an optimal diet but don’t overfeed them either!

With this guide on hand, you should be prepared to deal with any illness that befalls your guppies. I wish you good luck!

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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