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Best Comprehensive Guide to Aquaponics Grow Beds

clay pellets grow media
Rob Bob: RobsAquaponics.com

Everything You Need To Know About Aquaponics Grow Beds…

There are several key components of an aquaponics system that are essential to its operation, these parts are shared by all systems, no matter the type, size, or plants and fish you choose to raise. One of these is the aquaponics grow beds, which can vary in build and configuration depending on the type of aquaponics. As you may expect, the grow bed typically contains the aquaponics grow media, however, we say ‘typically’ because this isn’t always the case, at least not the same traditional sense as it may be utilized in other setups.

So while the concept of a grow bed is generally straightforward, the fact that may not be the same in all systems means you you’ll need to understand these differences so you can not only construct your setup correctly, but can also make the right, informed choice when deciding what technique to go for.

Firstly, since you’re reading this, it’s likely that this trend in eco farming is new to you, and that you’re just starting the enjoyable educative journey aquaponics is about to take you on, in which case, let’s cover the basics so you can easily see where grow beds fit and how they may differ from one another.

Table of Contents

What is Aquaponics, and What is a Grow Bed?

The Aquaponics Basics

Aquaponics setups are generally categorized into three types, with each having one, or more variations. The main three types of aquaponics are:

Nutrient Film Technique
– Can be configured into Vertical Farming Setups
Deep Water Culture a.k.a. Floating Raft Technique
– Has a passive alternative known as the Kratky Method
Media Based Technique
– Larger systems can be configured from IBC’s, sometimes referred to as the Chop and Flip method.
– Can also be configured as indoor gardens ideal for indoor aquariums. No matter the technique, all aquaponics systems cycle through three main processes – Fish Feed & Waste > Mineralization/Filtration > Plant Feed – and how the system is configured for each stage is what categorizes the type of setup, be it NFT, DWC, or Media Based aquaponics.

Aquaponics Stages… and The Grow Bed

The three main stages of all aquaponics systems include:

  1. The reservoir/tank for fish
  2. Mineralization tank
    Biofilter for beneficial bacteria
    – Solid Separator to filter water
  3. The grow bed contains grow medium for plants

The biofilter and solid separator make up the stage known as mineralization, which essentially filters the water and provides the substrate for beneficial bacteria to colonize and perform the all important nitrification process.

Each of these components is just as important as the next, and if you’re new to aquaponics then it’s a good idea to develop a comprehensive understanding of each type, stage, what it does, how it’s made, and how it works.

Furthermore, you’ll want to ensure you know how to monitor and maintain all aspects of your aquaponics system, from the components and parts to water quality and the living organisms in the ecosystem. Monitoring and maintenance are both vital to the operation and survival of your aquaponics system, therefore you’ll need to know how to spot when things are a miss, and how to rectify the issue as quickly as possible.

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What is a Grow Bed in Aquaponics?

As noted, and as you might imagine, the aquaponics grow bed is essentially the garden where you’ll plant and grow your chosen variety of flora. Aquaponics media grow beds are typically constructed as large plastic tanks, trays or channels, although these parts can be made from other materials including wood and metal.

The technique that utilizes the most traditional type of grow bed and grow medium is the Media Based method. This setup is most akin to soil setups, in which grow media replaces the soil, and these are typically the setups most growers refer to when talking about grow beds. We say ‘typically’ because the other techniques, NFT and DWC, utilize rather untraditional forms of grow bed; grow beds borrowed from the hydroponics growing method

These tend to utilize premade flat beds crafted from wood, chipboard and other paneling materials, or by using channels often cut from PVC piping. The grow media is then replaced with a grow substrate such as rock wool, grow sponges, gravel or expanded clay pebbles. Some setups can even have plants placed directly in net pots with, or without, without any grow media at all.

Aquaponics grow media comes in a number of different forms including:

  • Expanded Clay Pebbles
  • Gravel
  • Lava Rock
  • Coco Coir
  • Grow Stones

Is An Aquaponics Grow Bed Different From Traditional Grow Beds?

In the simplest of terms, and aquaponics grow bed is essentially the same type of grow bed used in hydroponics, at least for the NFT and DWC methods. The media based method however is more akin to soil-based grow, where the soil has been replaced with alternative grow mediums more suited to aquaponics.

The type of grow media, and its configuration, can affect a number of parameters in the systems, these can include:

The grow bed and media within is also one of the main areas the beneficial bacteria colonize to perform the nitrification conversion magic that keeps the ecosystem balanced and thriving. For this reason it’s extremely important to select the correct grow media for your needs. To achieve this you must first decide what system, fish and plants are your preferred choice, then tailor your grow bed media as best you can for the plants requirements.

Types of Grow Bed For Aquaponics

Media Based

As noted this technique calls for the more traditional grow bed setup, containing specific grow media known to be both suitable and effective for aquaponics. It’s this type of aquaponics that springs to mind when anyone mentioned aquaponics grow beds and grow medium.

Media based aquaponics systems can use a number of different grow media ranging from lava rock and coco coir, to expanded clay pebbles, gravel and grow stones. Each aquaponics grow medium offers different properties, and may, or may not, be more suitable for certain systems and plant species.

It’s also possible to find grow media with built in buffering capabilities, alternatively, the grow bed and media is a great place for the buffer to occur; essentially providing an extra level of caution by soaking up excess acid or base in your system and therefore giving you more time to spot the change and resolve the problem.

NFT

The nutrient film technique is an aquaponics method that doesn’t utilize an aquaponics grow bed in same traditional sense as media based systems. In fact the NFT name of the technique refers to the concept of the grow bed, which is typically constructed from PVC piping channels (check out our NFT DIY article for a visual) through which a thin film of water is consistently flowing passed the roots.

Vertical farming is also a type of NFT aquaponics. Although the setup lends itself to drip feeding nutrient-rich water to the plants instead of pumping a thin film along a horizontal channel, the concept still remains the in the NFT family of techniques.

In these systems the plants are commonly held in place by net pots, which usually contain a form of grow media to further support the roots, but not always, some plants can be placed directly into the net pots, or even directly into the channels themselves.

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DWC

Deep water culture, or floating raft systems, is another aquaponics technique the uses a non-traditional grow bed more closely resembling the concept of the NFT grow channels rather than the traditional grow beds and media of the media based systems.

In these DWC systems the plants are also placed and supported in similar way to NFT systems, by using net pots or directly into what functions as a grow platform, aka, the floating rafts; a simple floating board with holes drilled out to house net pots and plants.

For aquaponics grow bed DIY options, you can search online for used/second hand, repurposed or discount stock for all manner of PVC piping and its connections/fasteners, as well as scrap panel wood, cheap/discount chipboard, or any other cheap, lightweight material suitable for the task at hand.

Different Types of Grow Media

The Media bed/based system is synonymous with grow media, mainly because the latter two methods were developed directly from existing hydroponics setups and were specifically designed as soilless growing techniques that purposefully aimed to reduce the amount of grow media needed.

With that mind, the choice of grow media becomes a much more important one for media based aquaponics since the other techniques do not rely as much on grow media to support the system. As mentioned, there are several types of grow media suitable for aquaponics, and each has its own pros and cons. Popular types of gorw medium for aquaponics grow beds include:

Expanded Clay Pebbles

Often the most popular choice for aquaponics growers around the world, expanded clay pebbles are also known as Light Expanded Clay Aggregate (LECA), or just clay balls.

Pros: Clay pebbles and/or pellets are intert, lightweight, long lasting and even reusable. They provide lots of surface area for the beneficial bacteria to grow; they offer great water retention quality, which can help prolong the roots exposure to nutrient rich water when the cycle triggers the media bed to drain.

Like more types of grow media, the porous, uneven layers and the air gaps between the pebbles help to agitate the water as it drips and drains through the system to further aerate and inject additional oxygen into the water.

Cons: Unfortunately Light Expanded Clay Aggregate (LECA) is cheap, they’re also less capable of holding nutrients, which means you’ll need to keep on top of levels to ensure they stay consistent. And lastly, the some cases the plant roots can penetrate the clay balls and this can make it tough to separate should you need to clean, maintain, or remove the plant.

clay pellets 1
Clay Pellets at Amazon

Lava Rock

Also known as volcanic rock, lava rock is naturally derived from solidified volcanic lava. It is widely used in aquaponics systems thanks to the similar beneficial properties that make clay pebbels popular.

Pros: Lava rock is porous and lightweight, which just like clay pebbles, provides excellent aeration, sufficient area for bacteria to colonize, and effective water holding and draining capabilities for aquaponics grow beds.

Lava rock is slightly more durable than clay pebbles, and will not break down over time.

Cons: With similar pros to clay pebbles come similar cons. The composition of the material isn’t too effective for nutrient uptake. Despite being more durable, it is still somewhat susceptible to being damaged by the growth of strong, healthy plant roots that can crack through, and intertwine with the rocks. It’s also one of the more expensive grow mediums available on the market.

lava rock
Lava Rock at Amazon

Expanded Shale

Also known as lightweight shale aggregate, expanded shale is another commonly used grow media for aquaponics; also for beneficial properties that make it suitable for aquaponics grow beds.

Pros: Expanded shale makes up another lightweight and porous type of grow media. As noted, this helps increase aeration and DO in the system, whilst also providing ample room for the nitrifying bacteria to colonize.

The pH neutral shale is lightweight, durable, and offers fantastic drainage properties that can help prevent water logging.

Cons: Expanded shale also has limited ability to hold nutrients, and the cost can vary greatly depending on your location, which means you’ll need to perform the research to see whether the cost, and potential shipping fees, make it a viable option for your aquaponics setup.

expanded shale
Expanded Shale

Gravel

Pros: Gravel may not have the as many benefits as the aforementioned options, however what it does go well, it does better than any of the others. For example, since the rocks themselves are not necessary pourous, the mixture of different rocks, size and shapes creates a pourous structures that has unsurpassed drainage abilities.

Gravel is also more durable than the previous options, and will not noly last the longest in your grow bed, it’s also reusable if/when the time comes.

Cons: Gravel also has a low capacity for water retention, and depending on the type of gravel, it’s make up and the source, it can be prone to potential imbalance in pH levels.

gravel
Gravel

Factors to Consider When Choosing Grow Media

Regardless of the type of grow media you choose, there are a few universal factors you’ll want to take note of to ensure your system reaps produces the very best results. These can include:

Grow Media
Grow media can have an affect on some of the important levels you’ll need monitor and maintain consistently during the process. For example the grow media not only supports the roots, and allows nutrient rich water repeated exposure to these roots, the water cascading through the gaps in the media also help produce more dissolved oxygen to further aerating the system. Making and informed decision here as to what type of grow media is most suitable for your setup can and will make things easier and help you in the long run.

Dissolved Oxygen
An adequate supply of dissolved oxygen is essential for both the plants and the fish, so it’s important to remember that although new, clean grow media can promote aeration, over time the grow media can become dirty and even clogged, which will eventually lead to a decrease in the amount of oxygen being produced. Thus you’ll want to monitor and this regularly for any changes, so that you can clean when necessary, before it’s too late.

pH Neutral
Aquaponics grow media should be pH neutral, and non-reactive, that is, to not leach or release any harmful chemicals into the water.

Lightweight Grow Media
Another beneficial piece of advice would be to use lightweight grow media, which makes it easy for installation, maintenance, and replanting.

Grow Bed Depth
One of the next things you’re likely to ask is, “how deep should aquaponics grow bed be?” As you may have guessed, this would be determined by the species of plant you choose, and how big its root systems commonly grow.

But let’s say you’d like to change the species of plant with each harvest, but you don’t necessarily want to build a whole new grow bed or setup, then you can select a depth that’s likely to be compatible with most aquaponics plants; since these are typically short leafy greens, or smaller fruiting plants, an advise depth for your aquaponics grow media would be approx. 12-18 inches; generally enough to house the roots of most aquaponics plants.

Alternatively, you can opt to build an Intermediate Bulk Container based aquaponics system, also known as IBC Aquaponics or the Chop and Flip method. Since the grow bed will be constructed from part of the IBC, it can be easier to work out the depth, and therefore the volume of grow media required to fill the DIY grown bed.

In Conclusion

Although grow media is one of the most important choices you’ll make when setting up a media based aquaponics systems, it could be fair to say that there really isn’t an overall “best” option, Instead you should evaluate your situation, setup, requirements and goals, to help you decide what aquaponics grow media is best for you.

You’ll want to consider the type of pump and drainage system you use, for example, all four options work great with the installation of a bell siphon to automatically regulate water levels and drain when necessary.

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