How to Dramatically Increase Growth Rate of Guppy Fry?


Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate we earn from qualifying purchases. read more

If you are breeding guppies for fun or profit, most likely want to know how to increase the growth rate of your guppy fry. I was also struggling with this problem, but over the years have figured out how to grow my guppy fry fast and raise beautiful and healthy fish.

In this article, I will give you some very useful and simple tips on how you can also make your guppy fry grow faster. But first let’s see why your baby guppies are not growing. Here are the most common reasons why the growth of guppy fry is slowing down:

Top Reasons Why Guppy Fry are Not Growing

There could be several reasons, from genetics through water parameters to food that could affect the growth rate of guppy fry. I found that there are usually 3 main reasons why guppy fry do not grow as you want them to grow. Here are the most common reasons why guppy fry are not growing:

  • lack of water volume or too much water volume
  • lack of water changes and poor water quality
  • lack of quality and variety of food

Now let’s talk about each problem in detail.

Lack of Space or Too Much Space

Now you might call me mad. Why did I say too much space? Well, I found that very young guppy fry (up to 1 month old) will grow very slowly in a large tank. Due to high water volume, they are not able to find the food effectively. Fry will use a lot of energy to swim around and look for food. This energy can be turned into growth by providing the right amount of space.

The lack of space or water volume is also a problem. I’ve seen many guppy breeders, who were keeping their fry in breeder boxes until one month old. A breeder box is very small. Usually, it is around half a gallon or maybe less.


Keeping 20-30 fry in a breeding box for a month is a bad idea. Even if water flow is good, guppy fry won’t grow as you expect. So if you want some significant growth, do not keep guppy fry in a breeding box for more than a few days.

For younger guppies, under one month old, I recommend 0.5 gallon (2 liter) per fry. Above one month old, I recommend 1 gallon (4 liter) per guppy fry. The grow-out fish tank should be at least 5 gallon (20 liter).

Lack of Water Changes

Another common problem raising guppy fry is the lack of water changes. I can’t stress enough the importance of fresh water in a grow-out tank. Water changes are important, because this is the best way to eliminate the waste and toxins from the water.

Performing 1-2 smaller weekly water changes (15-20%) will help to keep waste at a minimum and will improve the growth of your guppy fry significantly.

Lack of Food Variety

Adult guppies will live and thrive on dried food. From time to time it is advised to mix up their diet, but it is not as important as for the fry.

If you want to raise healthy guppy fry, it is very important to feed them to a variety of food in order to avoid illnesses and provide them with all the minerals and vitamins.

Feed them live food daily and offer them dry food as well.

Best Ways to Make Guppy Fry Grow Faster

In the following, I will give you some tips on how to make guppy fry grow faster. Following these simple rules, you can achieve significant growth. I’ve used these techniques to raise guppy fry into adults in just 3 months:

  1. raise guppy fry in a separate tank and not in breeding boxes
  2. separate fry from adults or community tank
  3. separate fry by size and gender
  4. provide them with enough space and water volume
  5. feed regularly high quality and high variety of food
  6. do regular tank maintenance and weekly water changes
  7. don’t skip gravel vacuuming and filter maintenance
  8. combat despises and parasites as soon as possible
  9. treat diseases and parasites as quickly as possible
  10. use water conditioner to remove chlorine and chloramine
  11. keep water temperature stable at 75-78 °F (24-26 °C)
  12. keep the pH level stable: 6.8-7.8
  13. use a sponge filter to avoid strong water flow
  14. add live plants such as moss or guppy grass
  15. keep artificial lights on for 12-16 hours / day

Now let’s see each one in detail.

Raise Guppy Fry in a Grow-Out Tank

As mentioned before, the lack of space will slow down or stop the growth of the fry. Do not us a breeding box to raise your guppies. You might keep them there for a few days, but remove them from the box as soon as possible.

Raise the Fry Separately

Do not mix guppy fry with their adult parents. Raise them separately in a grow-out tank. Adults won’t stress them out, and they won’t need to hide from bigger fish.

Raising them separately will reduce stress and competition for the food and will also help with the growth rate.

Separate Fry by Size

It is also a good idea to separate the fry by size and different age broods. Bigger fry are more agile and will eat more. The tendency is that the bigger ones will get even bigger and the smaller fry will remain smaller.

While raising the fry in a grow-out tank can add a lot to the growth rate, raising each batch separately is even better.

Separate Fry by Gender

Separate the fry by gender is a must if you want to grow your guppies faster. This is not an option right from the beginning, because it is impossible to tell the gender of a one week old guppy fry. But as the fry grow, you will be able to sex them easily and relocate them into other tanks where females and males are kept separately.

In just 3 months your fry will try to mate, wasting huge amounts of their energy. Keeping them separately they will grow healthier and faster.

Give them Enough Space

Personally, I recommend 0.5-1 gallon (2-4 liter) of water volume per guppy fry. While the fry are younger, up to 1 month old, half a gallon of water per fry is enough. For fry that are older than one month, I recommend 1 gallon per fish.

Here is a great video that shows the amazing growth results by keeping guppy fry separately:

Feed Regularly with Quality & Varied Food

Feed the fry 3-5 times a day with high-quality and varied food.  I prefer to feed live and home-made food instead commercial food. I understand that not everyone can cultivate their own live food or can’t prepare the food for their fish. In this case you can choose commercially available food. If you do so, only buy premium food from well-known brands.

If you don’t have time to feed the fry multiple times a day, you can set up an automatic feeder, which will feed them dry food.

Read my other article about guppy food, where I share a secret guppy fry food recipe that will dramatically increase the growth rate.

Perform Small Weekly Water Changes

It is very important to do regular maintenance on your fish tank and do weekly water changes. This is the best way to remove the toxins that are accumulating in the water throughout the week.

If you are feeding your fry heavily (4-6 times a day), waste and toxins will accumulate much faster. In this case you might want to do 3 smaller water changes of 15-20% weekly.

If you feed your guppy fry 3 times a day, 2 partial water changes of 15-20% per week will be enough.

Filter Maintenance & Gravel Vacuuming

The weekly water changes are not enough. A lot of muck can build up in the gravel and filter.

If you keep bare-bottom tanks, the waste is very visible at the bottom of the tank. The substrate will hide all the fish waste. If you don’t see the waste, it does not mean it is not there. It is there, under the gravel and is pollution your water. It is very important to perform regular gravel vacuuming.

Also it is very important to clean the filter on regular basis, because filter can be also a great source of pollution for your aquarium water.

Control Diseases and Parasites Quickly

Even though you are not bringing fish from other sources or you quarantine them for 3-4 weeks, diseases and parasites can still occur in your tanks.

You can introduce the illness into the tank through water changes, through food, dirty hand or who knows how.

There are many diseases that cannot be treated, but can be prevented with regular water changes and quality food.

Inspect your guppy fry regularly and if you see any anomaly or random deaths, dig deeper. Dieses and parasites should be treated quickly with the right medication.

Unfortunately I’ve learned this the hard way, when a camallanus worm infection wiped out my entire guppy colony.

Please read my detailed article about guppy diseases, parasites and illnesses.

Condition the Water Using Water Conditioners


If you are using tap water for your tanks, a water conditioner is a must for you to remove chlorine and chloramine as well heavy metals.

Always use premium water conditioners such as Seachem Prime. A bottle of 500 ml of Prime can treat 5,000 US gallons of water. Very cost-effective way to ensure your fish health.

If you have a well, and the water is safe for drinking, I still recommend using a water conditioner. Also test the well water for ammonia, nitrites and nitrates.

A friend of mine has been struggling for more than a year to figure out why the nitrate levels are ridiculously high in his fish tanks, even after water changes. Through some tests, he found out, that the water from his well had a 20 ppm nitrate level. The water was safe to drink, but not so safe for keeping fish.

Always Use Water from Same Sources

Although guppies can support a wide range of water parameters, they are very sensitive to huge fluctuations.

If you use tap water for weekly water changes, do not change it drastically to well or rainwater. Make sure that the transition is smooth, so the fish can acclimate to the new water.

Keep Stable Temperature

Guppies can live in waters with temperatures between 65-85 °F (18-30 °C). However, for optimal growth and health, I recommend keeping and raising guppies in water with temperatures between 75-78 °F (24-26 °C).

As mentioned before, guppies hate fluctuation in water parameters. So try to keep the temperature as stable as possible. The best way is to keep the aquarium in a room, where the temperature is stable, so the temperature of water can also remain stable.

Check Water Parameters

Water hardness is not very important for guppies, but I like to keep it between 150-450 ppm. This gave me very good results over the years.

For best results and growth rate keep the water pH between 6.8-7.8 level.

Reduce Water Flow

Guppy fry are sensitive. Swimming against strong water currents will make them consume a lot of energy and eventually exhaust them.

Do not use a powerful internal or external filter; instead use a simple sponge filter. An air-driven sponge filter will provide just enough water movement, but not a strong flow.

Add Live Plants

I see many guppy breeders use bare bottom tanks with no aquarium decoration. Don’t get it why is necessary to keep your guppies in such a sterile environment.

From my experience adding plants to your breeding and out-grow guppy tanks is also a contribution to growth and health.

Nitrates are the “final product” of fish waste, which in high quantities is toxic to your fish. Live plants will consume nitrates from the water columns, “purifying” the water.

On the other hand plants can provide surface area for microorganisms and algae to grow. Guppy fry will graze on plants all day long and will eat anything they see. This is a great way to extend the feeding period of the fish.

The best plants to keep in guppy fry tanks is java moss, guppy grass and java fern. These plants are very easy to care for. Do not require special lights nor fertilizers.

Guppy Grass
Java Moss

Keeping live plants in your aquariums is also good for preventing or reducing algae growth, because plants and algae are competing for resources.

Increase Time of Artificial Lighting

Another great way to increase the growth rate of guppy fry is to have artificial lighting. Keep the lights on for 12-16 hours a day in order to achieve the best results.

Do not keep the lights on 24/7, because just like humans, fish also need to rest. Guppies need darkness in order to sleep and they need at least 6 hours a day of darkness.

I recommend keeping the lights on no more than 16 hours a day and give them time to sleep.


So here you have my top tips that will help you grow your guppy fry faster and healthier. I’m using these techniques myself and got some really good results.

As mentioned before, in just 3 months my guppies have grown to sellable sizes.

I hope that you will also achieve these results by using these simple tricks.

Also, I would like to know if you have heard or have been using other tricks to grow your guppies faster and bigger. Please share your thoughts below in the comments, or send me an email through the contact form.

Updated: October 18, 2021
Questions & Answers
Leave a Comment

Your email address will not be published. Required fields are marked *