Why Do My Guppies Die After Giving Birth

If you just started breeding and your guppies die after giving birth- you’re not alone.

You may already know by now- but in case you don’t- I don’t like long intros. 

So without further ado, let me teach you why do your guppies die after giving birth, and what can you do to prevent it. 

TL;DR Summary

Why Do My Guppies Die After Birth

There could be multiple reasons why guppies die after birth: 

  • Poor water quality– like ammonia, nitrate, nitrite, pH, and temperature
  • Bad nutrition
  • Aggressive tank mates– this can come from males, females, or other fish altogether
  • Stress– could be due to overcrowding, water parameters

The 3 Reasons Why Your Guppies Die After Birth

Why Your Guppies Die After Birth

Poor Water Quality

We’ve mentioned the 5 water parameters in the summary, but let’s take a closer look into each one of them.


Ammonia is naturally occurring when organic matter decompose.

What organic matter? Oh, it’s stuff like:

  • Fish poop
  • Leftover feed
  • Decaying plants decompose. 
  • Dead fish at the bottom of the tank

The best way to go about ammonia is to measure it using a testing kit first.

What's the max ammonia for a guppy tank?

0. You should have no detectable levels of ammonia in your tank. 

If you see ammonia presence in your tank, change 50% of your water, wait 24 hours, and test again. 

If the issue continues, it might have to do with the substrate not being cleaned often enough or your biofilter being faulty. 


Nitrate (NO3-) and nitrite (NO2-) are both forms of nitrogen compounds that can be present in a fish tank. 

While nitr(a)te is relatively less harmful to fish, nitr(i)te can be highly toxic. 

In the nitrogen cycle, beneficial bacteria called nitrifying bacteria convert toxic ammonia (produced from fish waste) into nitrite and then further oxidize nitrite into nitrate.

Nitr(a)te is less toxic and can be utilized as a nutrient by plants in planted aquariums.

Any level of nitr(a)te above 25 ppm,  can cause stress, and impaired immune function.

And Nitrite

Nitr(i)te is produced during the initial stages of the nitrogen cycle when ammonia is broken down by nitrifying bacteria. 

Nitr(i)te is highly toxic to fish, even in small concentrations and the reason you’ll end up with nitr(i)te is if your biofilter is faulty. 

Nitrite interferes with guppies’ blood’s ability to transport oxygen- which leads them to drown. Even the lowest levels of nitrite (above 0.1 ppm) can cause stress, respiratory issues, and organ damage.

Pro Tip

Confused about the different between nitrate and nitrite?

A Is Okay, Buy I Doesn't Fly
How to lower nitrite levels in a guppy tank

You can lower nitrite levels by following the 3 following steps:

  1. First thing first- perform partial water changes immediately to dilute the nitrite concentration. I would do at least 50% and replace it with conditioned, temp-matched water.
  2. Second, ensure that the aquarium is properly cycled, allowing beneficial bacteria to convert nitrite into nitrate. Adding nitrifying bacteria supplements or increasing aeration can expedite the conversion process.
  3. And last, you can limit feeding temporarily to help reduce the production of nitrite. Guppies are hardy fish and can go a long time without food

pH Levels

pH levels are usually a byproduct of other processes that are happening in your tank. 

If your pH is high (over 8):

Increase the amount of CO2 in the tank. This can be done by adding driftwood, peat moss and a CO2 reactor to the tank. 

If your pH is low (under 7):

Add baking soda to the tank.

If you suspect that pH is the culprit then look at our complete guide to guppy pH water control

Water Temperature Fluctuation

Guppy fry need a constant temperature between 74-82 degrees to thrive. 

Remember that both adults and fry are highly sensitive to temperature changes. A good rule of thumb is to only change the temperature by 1 degree every 24 hours.

If you need to do a water change, the best practice is to just keep an extra tank worth of ready-to-use water, which is already conditioned and brought to temp. 


Poorly Maintained Substrate

Accumulated debris, uneaten food, and waste in the substrate can decay and release harmful substances into the water column.

Regular substrate vacuuming during water changes helps remove these accumulated materials and prevent water quality issues.

Is Bad Food Why You Guppies Die After Giving Birth

Pregnancy could very physically demanding of guppies.

I’ve seen females go both ways when pregnant- either developing a loss of appetite or becoming hungrier than ever- so there’s no “regular” behavior. 

So let’s take a look into what you should be feeding your guppy after birth. 

High-Quality Fry Food

Guppy fry have small mouths and require food that is easy for them to consume. Look for specialized fry foods available in pet stores or online.

These foods are typically formulated to meet the nutritional needs of developing fry and are often in the form of powdered or finely crushed pellets.

Commercial Fish Food

Pellet, flake, tablet- pick your favorite. As long as it’s for tropical fish- you’re good.

The reason I bring up tropical fish is that this food is higher in protein- which is what your guppies need. Feed her just like the others- about 2 to 3 times a day in small portions that she can finish in under 3 minutes.

Live Food

I’ve covered in great detail all the live food options for guppies, but to save you the read- brine shrimp is my favorite.

Other stuff like daphnia, vinegar eels, or microworms will work. Those the the preferred foods by guppies- but they require a little bit more prep compared to commercial food. 


Spinach, cucumber, carrot- the list goes on and on. 

The upper 2 are definitely preferred because of their high protein contents, but vegetables can be fed to your postpartum guppy. 

Supplementary Foods

I think supplements are one of the biggest kept secrets on guppy fish keeping.

They are packed with vitamins and minerals, plus they increase the amount of zooplankton in the water. 

Guppies actually eat zooplankton, but there’s really no way for it to get into your tank without you adding it. 

Are Aggressive Tank Mates Why Your Guppies Keep Dying After Birth?

Here’s the thing-

Guppies can really go either way with pregnancy- the pregnant female and become aggressive, or she can be the victim of aggression. 

You can’t really fix her if she’s the aggressive one. You can try putting in a birthing tank- but that’s a short-term solution. 

Your best bet it to make sure the tank has plenty of hiding spaces- be in the form of plants of aquarium decoration. 

Side Note

In some cases your guppy may feel the tank is overcrowded- which will trigger stress. 

Overcrowding happens when you have too much fish, but what beginners usually forget to account for is vegetation.

If your tank is packed with vegetation and takes more than 40 percent of your tank- you may need to re-think your setup. 


The main 3 reasons why your guppy may be dying after birth are:

  • Bad water
  • Bad nutrition
  • Stress & aggression

All 3 will call for different solutions, which luckily aren’t too complex to execute.

Your best strategy, regardless of the problem and the solution, is to monitor the tank. 

The more you understand the baseline behavior of your guppies- the easier it’ll be for you to identify the problem. 

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