Why Do My Guppy Fish Keep Dying? {9 Possible Explanations}

There’s nothing more provoking than looking into your tank to see one of your guppies floating lifelessly at the surface of the water. Why do my guppy fish keep dying?

Do you need a list of possible reasons with explanations. I’ve been through this before and I’m happy to help.

This article is for all the guppies who passed away and how to help yours live longer.

Why Do My Guppy Fish Keep Dying?

The most common reason for guppy fish dying is poor water quality.  They require warm water temperature and well oxygenated water. It is also recommended to treat the tap water you put in your tank as this can also be the cause.

9 Possible Explanations:

  1. Bad Water Quality
  2. Not Enough Water Changes
  3. Stress
  4. Overcrowding
  5. Insufficient Chemical Filtration
  6. Shortage of Warmth
  7. Contaminated Water
  8. Sickness
  9. Parasites

Allow me to elaborate on these possible reasons below:

Why Do My Fish Keep Dying?

Why Are My Guppies Dying One by One?

This might be a case of “Fresh Tank Syndrome”.

This is the theme that is used when fish become sick or die in a newly constructed tank/aquarium. It is normal for fish to produce ammonia, and this is formed when waste is released into the aquarium water by the fish.

Surplus fish food and debris also rot in the aquarium, and this too can escalate ammonia levels.

Fishless Sequence

Some people select to do a fishless sequence when they first purchase an aquarium to establish the aquarium and organize it so that it is a safe environment for fish to grow well once they are introduced.

A fishless sequence can be a complicated process, but it involves imitating the changes that would occur when fish are added to an aquarium – but without the fish.

This means that you need to introduce ammonia to the aquarium yourself to develop the filter so that when you introduce the fish, the area won’t cause them any harm.

Within 7 Days

Moreover, most of the people add their first fish to a tank within seven days after setting it up, without any issues. Problems can arise, though, if your tank/aquarium is not correctly cared for. If you’ve newly lost fish or your fish have become sick, here’s our guide to possible problem causers.

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How Water Quality Kills Guppies

The kind of water in the tank plays a big part in the growth of your guppies, and if it is not up to solve, your fish can pay the critical price.

Ammonia and nitrite are just two of many common issues that you might come across while caring for a tank, and both can affect your fish.

Many things can lead to ammonia, such as fish waste, remaining rotten food at the bottom of the tank, and dead fish not being removed quickly. Overfeeding your fish is a practice that is worth circumventing.

You can check the water quality of your aquirium by using a testing kit such as API phosphate test kit

How Many Water Changes For Guppies?

If you don’t conduct steady water changes, then fish waste and surplus food will remain in the aquarium.

A fish tank filter plays a huge part in eliminating food and waste, but it can still help to frequently add fresh water so that issues don’t keep circulating.

Water changes need to be done at least once in 5 to 7 days, and you should get into the routine shortly after buying your fish tank, rather than waiting for issues to arise before you start to alter your tank water.

To make sure that your water value is good enough for your fish, using a test kit often can be helpful.

Why Do My Fish Keep Dying?

Are My Guppies Stressed?

It may shock you, but just like humans, fish can become strained quickly, and this can be bad for their well-being.

The more stress they go through, the more prone they are to being affected by diseases, and the more they tussle to fight these sicknesses.

Stress can be caused by disorders such as:

  • loud noises
  • needless substrate changes
  • hands being placed in the fish aquarium
  • bullying from other guppies.

It’s best to avoid troubling the fish tank unless necessary.

ALSO READ THIS, Do Guppies Sleep At The Bottom of Tank?

Are My Guppies Overcrowded?

Overcrowding is a famous fish killer. Many tank owners can get carried away when buying fish, buying far too many for the size of the aquarium you have constructed.

This not only gives the fish fewer space to move around in, but it also raises the chance of there being an ammonia issue. A good rule to follow is just one centimeter of fish per liter of water in a tank.

This aids you to work out a lot of fish you can stock while taking on board, but be aware that not all fish are the equal size.

What Happens When You Add Too Many Guppies?

Even if you don’t have a lot of fish in your aquarium, adding numerous fish at once can lead to high ammonia levels, while a rapid and dramatic change can kill the fish off fast when they don’t have clean water to swim in.

It’s best to slowly introduce your fish to the tank a few at a time, making sure that you acclimatize them correctly. 

You may be concern that your fish are starving and will die if they aren’t well fed. But it is more harmful to feed your fish excessively.

Overfeeding Guppies

Overfeeding is a common issue, and it can be risky even if you’re only guilty of it on occasions.

Leftover feeds will sink to the bottom of the fish tank and will progressively rotten, increasing the amount of ammonia in the aquarium.

One way of sucking up all of the rotten food is by including a bottom-feeding fish like a catfish to clear uneaten food, but you must be sure they won’t feed on your guppies.

Regular water variations can also help to reduce any effects of overfeeding. We know prevention is better than cure, so it is fine not to overfeed in the first place.

4 Reasons Why Guppies Die

1. Insufficient Chemical Filtration

Remember to apply a de-chlorinator and strain coat when doing a water change to make sure that the water is harmless for the fish. Putting water straight from the tap without treating it first is a typical destroyer of fish.

2. Shortage of Warmth

If you have humid fish, you need to sustain a certain temperature to make sure that they don’t get too cold. Fish tank heaters do this seamlessly, and the majority will control themselves to make sure that the water doesn’t get too warm or cold.

3. Contaminated Water

Water can become polluted quite easily, and the slightest trace of imported material can cause issues for the tank dwellers. One of the most known ways a fish tank can become polluted is when you are changing the aquarium water or during feeding.

We advise using the same plastics for water changing and working at the aquarium. Never wash this plastic/bucket using cleaning reagents as the smallest drop of washing up liquid can pollute the water, for instance. Water can also become polluted if you add the water directly from the tap without using dechlorinator to eradicate chlorine and other toxins.

Why Do My Fish Keep Dying?

4. Sickness

When an illness starts to take hold of your fish aquarium, it can be hard to control, and before you know it, you can lose many of your fish within the shortest time, and in really severe cases, you lose your guppies in hours.

Happily, almost all fish diseases, parasites, and bacteria can be healed with treatments and drugs. Ensure you don’t over-medicate, though, as this can lead to more harm than good.

Disease handling can be a valuable addition to your aquarium kit when your guppies start to get sick or if they give up the ghost. Some treatments can target the problems and stop them from spreading.

But first, you should work out precisely what sickness it is that your fish are suffering from.

Common Fish Diseases In Guppies

1. Parasites

The popular NT Labs Formaldehyde is an awful disease treatment to defeat parasites and flukes. It can be mixed with NT Labs Malachite to fight parasite infections such as Ichthyopthirus white marks/spot, Trichodina, Costia, and Epistylis.

2. Anchor worms 


  • Rubbing against objects in the tank
  • White/green threads evolving from scales
  • Swelling of the scales where threads appear

CHECK OUT, How Can You Tell A Male Guppy From A Female Guppy?

How To Help Sick Guppies

Anchor worms, peel worms, gill worms, and the usual tapeworms can all be eliminated with the precise dosage at regular breaks. It’s vital to follow the guidelines on each container of medication.

If you have lost some fish in a short space of time, it might be due to coincidence. Many species of guppies only live within a year or three years on average, meaning that death is unavoidable at some point.

It is imperative to keep an eye on their sickness in case there is something in the tank that is affecting the guppy fish and killing them.


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Hello, I'm Jason. I'm the guy behind HelpUsFish.com. I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.