Aquaponics Growing Medium: What Are They and Why You Need Them

Aquaponics Growing Medium: What Are They and Why You Need Them
External Guest Writer
April 27, 2021

The aquaponics industry has been slowly expanding its reach and scope over the last decade. It is possible to understand the scope of this industry by looking at the global net worth of aquaponics and its steady expansion. In 2018, the industry was worth over USD 600 million, but forecasts predict a CAGR of 15.5% all the way till 2025.

This alludes to the fact that aquaponics is on the rise, as it well should be. There is tremendous value in modern farming systems that allow for soilless agriculture, and aquaponics is leading the way in that regard.

In this article, we highlight one of the chief components of aquaponic farming — growing mediums. We discuss the specifics of growing mediums, its place in aquaponics, and highlight the best aquaponic grow medium to be used in this industry.

What is Grow Media?

The growing media is undoubtedly one of the most vital components when it comes to conducting farming without the use of natural soil. Although grow media aren’t utilized in all forms of aquaponic farming such as the floating raft system, they form an integral part of nearly most forms of agriculture in this system.

Growing media is the substitute for soil used in aquaponic farming in order to provide nutrition to the plants. There are numerous reasons why growing media is essential to an aquaponics system, and we discuss these reasons in the section below.

Why Do You Need It In An Aquaponics System?

The major purpose of using an aquaponic grow media is to provide a safe location for the roots of a plant. The root structure of a plant is absolutely crucial in dictating the future health and wellbeing of the fruit or vegetable. All of the nutrition supplied externally by farmers are absorbed using the roots itself, and thus it is important to always ensure the safety of the roots.

Additionally, the roots also help the plants balance their weight and act as a support system when they are ready to grow beyond a sapling. 

By using an aquaponic growing media, it becomes possible to help support the roots in all their intended endeavors. The media will help keep the roots in place and allow them to improve on their stability. It also acts as a source of nutrition, allowing the roots to gradually absorb all the essentials that have been placed in the growing medium by the farmers.

Another crucial factor that makes aquaponics grow media an invaluable cog in the setup has to do with the surface area provided by the medium for the growth of bacteria.

Aquaponics is highly dependent on the bacteria that naturally develops within this ecosystem in order to support the plants. The bacteria play a vital role in this process as they help convert the fish waste into nitrites and eventually into nitrates that are absorbed by the plant.

In order for the nitrifying process to occur, however, the bacteria require a surface to hold on to as they attempt to develop in the aquaponics system. The bigger the surface area, the higher the number of bacteria that can develop internally, thereby leading to improved ammonia conversion. 

Growing media is also important in a flood and drain aquaponic system as it allows for the development of a large root system and also offers plenty of surface area for the development of bacteria.

Requirements for Grow Media

There are plenty of options available for the modern aquaponic farmer in terms of selecting a growing medium. There are, however, a few important criteria that must be considered before finalizing on a grow media.

Easy to Handle

When you intend to position the growing medium in your grow bed, you will need to manually handle the material for a considerable period of time. Thus it can be convenient to pick a medium that’s easy to handle and is also easy on the hands of the farmer. 

Lava rocks, for example, are a popular choice of grow media because they have a large surface area and are more porous than most of the other options available in the market. Unfortunately, these rocks are also quite sharp around the edges and can lead to frequent cuts if the user isn’t careful. This is why it’s important to wear a pair of high quality gloves while using this medium.


Based on the size of the aquaponic farm and the type of plants being grown, the price of the medium is also a necessary factor to consider. Balancing the budget for the growing medium with the expected income from the produce is an important facet of aquaponic farming.

For example, gravel is the go-to medium of choice when looking for a cheap and effective grow media. Hydroton, on the other hand, is an expensive option that tends to provide excellent results. When growing premium produce, hydroton would be the media of choice in order to maximize the potential of the plant.

See also: Agricultural Grants for Aquaponic Farming

Increasing Surface Area

As previously mentioned, the surface area of the growing medium is directly related to the amount of bacteria produced in the system. If the level of bacteria in a system is on the higher end, it will be hugely beneficial to the conversion of ammonia to nitrates in order to nourish the plants. 

Every growing medium has its own differing surface area. Recognizing the strengths and weaknesses of each of the mediums will allow you to find the idea option for your needs.

Ph Levels

The pH levels in an aquaponic system need constant monitoring in order to preserve the overall health of the plants. The pH requirements for fish tend to be different from the pH requirements of plants, although it is possible to pick up fish and plants that require similar pH levels. Ideally, a pH level of 7 is what one should strive for once the system is up and running.

Based on the type of grow media employed in an aquaponic module, the pH levels may also get altered accordingly. Some grow media can greatly diminish the overall pH level of a system and can thus end up damaging the health of the plants and fishes. 

Limestone, for example, is a type of media that is used to raise the pH levels of a system. 

A great way to check the effect of a grow media on the pH levels is by using vinegar before placing it in the system. Washing the medium thoroughly and placing it in a container with ample vinegar covering the medium is a great test in this department. 

If there are bubbles formed after the addition of vinegar, it implies that the pH levels are on the higher end of the scale. This is because the bubbles tend to read with the vinegar in order to induce bubbles.


Every growing medium decomposes at a variable rate based on its internal composition. The rate of decomposition influences the surface area on offer for the growth of bacteria. It also has an impact on the maintenance of the aquaponic module as constant decomposition can lead to blockages in the pipes. Thus it is important to pick up a growing medium that decomposes at a natural rate.

The Best Aquaponics Grow Media

In this section we look at the top growing media available for aquaponic farming. We also highlight the features of these media to help readers make an informed decision.

Lava Rocks

Lava rocks is one of the most popular choices when it comes to purchasing cost-effective but efficient growing mediums. These rocks are formed when the red hot lava from volcanos cool down and condense rapidly. The air pockets that are trapped inside the lava rock help to increase the overall surface area of the medium, and this has a positive impact on the bacteria growing in the system.

The air bubbles also help to bring down the overall weight of the rocks and this helps to improve the drainage capacity of the medium. 

Another major advantage of Lava rocks is that they are pH neutral and thus no preparations will need to be made in order to use the rocks in your aquaponic system. 

One of the setbacks of this medium, however, is the fact that they have sharp edges, and this can be harmful for those who have to tackle this medium on a regular basis. It is always recommended that a person uses a strong and reliable pair of gloves before working with lava rocks


Hydroton is a high quality choice when it comes to picking a growing medium for your aquaponic system. It has a large surface area when compared to other alternatives, but comes with a downside with regard to its price tag. This is one of the more expensive mediums on our list.

When looking at the composition of hydroton, it is clear that this is a type of expanded clay product. Clay is an excellent medium for growing nearly any type of fruit or vegetable. This is because clay is a naturally porous material and its microscopic holes allow for excellent drainage while also having the ability to hold plenty of water. 

Thanks to the many tiny holes in hydroton, the surface area of the growing medium tends to increase substantially. This helps to improve and control the growth of bacteria within the module to help boost the nitrifying process.

Hydroton is also a pH neutral medium which means that no prior preparations are necessary to use the medium. 

One of the downsides, however, of Hydroton is the fact that it tends to float when placed in water for the first time due to its porous and lightweight nature. If these floating bits of hydroton aren’t controlled, it can lead to blockages within the filters and pipes.

Pea Gravel

For those on the lookout for a growing medium that’s extremely cheap, pea gravel is often the first name to come to mind in this department. The name pea gravel comes from the size of each piece of gravel that is often extremely small and rounded. 

The material, however, can come from any type of gravel, which is why it is important to check the type of pea gravel before making a purchase. Ideally, pea gravel made from quartz tends to have all the qualities required for aquaponic farming. Limestone pea gravel, on the other hand, tends to have high levels of pH and are not best suited for this method.

One of the greatest strengths of this medium is the pea-sized gravel itself that tends to offer a large surface area for bacteria. This is hugely beneficial for the nutrition of the plants in the long run.

River Rock

River rock is a type of grow media that’s not only cheap to acquire but is also readily available in most locations around the planet. These are rounded rocks that have been shaped by the force of flowing water in a river.

As these are relatively cheap variants of growing mediums, they are often available for purchase in a wide set of price points. It is always recommended to at least opt for a mid-grade version of river rock for the sake of longevity. 

The lower grades tend to have rocks that are too small for aquaponic farming. These small rocks can lead to clogs in the growbeds and will subsequently require a lot of maintenance. Going with extremely large river rocks is also a problem as it tends to dramatically lower the surface area required for the growth of bacteria.

River rock is usually the preferred choice by individuals new to aquaponic farming. 

This medium does have its own set of downsides to consider as well though. First of all, river rocks aren’t pH neutral which means that a set of tests will need to be conducted before applying them in your aquaponic farm. 

It’s also important to remember that river rock is generally heavy and will need to be placed intelligently so as to not overburden the grow bed.

Expanded Shale

When natural shale is heated to high temperatures (as high as 2000 degrees fahrenheit), it leads to the creation of expanded shale. During this expansion process, there are numerous tiny pockets of air created within the material that aids in the aquaculture process. This helps to boost the porous properties of the shale in addition to increasing the surface area as well.

Expanded shale is also one of the cheapest grow mediums in the market currently and is usually priced on par with pea gravel. Thus it is a widely considered option as it has fewer disadvantages when compared to pea gravel.

The only major downside of pea gravel is the rough and hard edges that may cause injuries to individuals who frequently handle the medium. Using a pair of tough gloves should help to tackle this issue though.

Clay Pebbles

Lightweight expanded clay aggregate (LECA) or clay pebbles are balls of clay that have been tempered with high temperature in order to create an important grow media. These are light enough to be used for aquaponics but heavy enough to also support the roots of the plant.

Additionally, this medium is non-degradable and pH-neutral. The poros makeup and spherical design also helps in maintaining the oxygen levels in the water. 

The fact that this media is made out of clay also ensures that this media is easy to work with by hand. The soft and rounded surface does not pose any threat to individuals working with clay pebbles on a regular basis. 

The only downside here is that this is an expensive medium and one should analyse the cost-benefit ratio before finalizing on clay pebbles as their medium of choice.

Hydro Stones

Finally, we have hydro stones or growstones. These are a type of grow media that are porous and lightweight and are predominantly made using glass products that have been recycled. The manner in which hydro stones are produced itself ensures that this media turns out to be pH neutral. Not only that, but the process of creating growstones emphasizes on improving the pores in the material to make it all the more handy when it comes to nitrifying bacteria.

The surface area of this material, however, is on the lower end of the spectrum. It feels very similar to sandpaper and can be difficult to handle due to its rough edges. Additionally, this media is not freely available as it is a specialist option used specifically for aquaculture.

Aquaponic Growing Medium

Aquaponics is a method of farming that is currently rising in popularity around the world. Due to this, there are more options in the types of available growing medium than ever before. There is also ample information available to help farmers ascertain the ideal growing medium for their farms.

Once the right medium has been applied in an aquaponic farm, it greatly boosts the health of the plants and ensures that a vital cog of an aquaponic module is firmly in place.