What is a Media Based Aquaponics System?
Media Based Systems, also called Flood and Drain,” or “Ebb and Flow” are the most common Aquaponics systems, popular with do-it-yourselfers, backyard home systems, and commercial farms. In a media-based system, plants are grown in a planting media such as gravel or expanded clay pebbles. The media filters ammonia-based fish waste and solid waste. This system is well suited for growing larger fruiting plants as well as smaller plants.
How Media Based Aquaponics Systems Work
The Media-Based System uses media filled grow beds or containers filled with a suitable growing media such as expanded clay pebbles, lava rock/pumice stones or gravel. The water from the fish tank is pumped over to the media filled beds, and the plants grow in the clay or rock media.
The water from the fish tank is pumped or drained to the grow beds so the plants can access the nutrients from the water. The gravel or clay pellets hold the water longer to remain aerated and for more efficient nutrient ingestion. The gravel or clay pellets also serve as a filter for organisms, parasites, and other solid materials; and prevent them from going back into the fish tank. The clean water is then drained back into the fish tank.
This system can be run by flooding and draining the grow beds, using a bell siphon to drain the water when it reaches a saturation point.
Once the water reaches a certain level on the grow bed, the bell siphon will drain the water from the grow bed. This process will draw oxygen back down into the grow bed for the benefit of the microbes and the plants. These are a continuous regular cycle that provides all the necessary nutrients for the plants to grow without the use of fertilizers.
Components of a Media Based Aquaponics System
First and foremost, one of the essential components in the media-based system is the grow bed. The grow bed is where you grow your plants. Make sure your grow bed is:
- made of food-grade materials that will not leak unwanted chemicals into the water, or that will affect the water pH.
- Strong enough to hold the water and growing media.
- Able to withstand different weather conditions.
- It can be connected to other components easily. (1)
Grow Bed Sizes
A media-based grow bed needs to have the right depth and size in relation to the fish volume and to provide adequate filtration for the nutrient-rich water. The standard grow bed shape is rectangular and raised off the ground for easy maintenance.
Grow beds should be about 12 inches in depth to optimize plant growth and for the cultivation of beneficial ecosystem in the bed. When selecting your grow bed, the rule of thumb is to use a 1:1 ratio of your grow bed to the fish tank in small systems. These means that the grow bed volume should be equal to the fish tank volume. These are not a hard rule but a good rule to follow when starting. (1)
Grow Bed Zones
There are three grow bed zones in the media-based system, and each zone has different functions in the system.
Zone 1 - The Surface or Dry Zone. This area is within the first 1- 2” (5 cm) of the grow bed. This area is called the dry zone and functions as a light barrier, preventing the light from hitting the water directly and preventing the growth of fungus. This area minimizes evaporation and prevents collar rot and other plant diseases.
Zone 2 - The root zone. These are where the plants’ roots grow and where all pants activity takes place. Zone 2 is around the 4 - 6” (10-15 cm) area of the grow bed and is the area that is regularly flooded and drained. (2)
When it’s time for the flood and drain cycle, the drain parts allow the water to drain away completely. This draining provides for the efficient delivery of the oxygen-rich air into the plants' root area.
For the flood and drain cycle, the incoming water helps spread moisture, nutrients, and incoming solid fish waste particles into the area. In this area, the worms are responsible for breaking down and minimizing solid waste, which in turn releases nutrients throughout the system.
Zone 3 - The solid collection and mineralization zone. This is the last zone, which is in the last 2” (5 cm) of the grow bed. This is where the fish waste, other solids, and worm castings are collected in the system. (2)
Many materials can be used as a medium in a media-based system. The media must be organic and have an adequate surface area to allow bacteria to grow and water to flow to the plants' roots. The media must have a neutral pH so that the water quality will not be affected. It is good to wash the media thoroughly before placing it into your grow bed to ensure that there are no dangerous particles that can potentially harm the fish.
Grow Media Options
Gravel: Is the least expensive and most readily available grow media, ¾” Gravel is best for supporting taller plants, and it doesn't get clogged like smaller pea gravel. Gravel, though, is heavy and is not as preferred for growing smaller plants because it can be rough on the hands. Another drawback of using gravel is that it does not hold water efficiently, so it can sometimes be more challenging to colonize the needed bacteria in your system. It is important to perform a vinegar test of gravel before placing it in your system, as limestone is sometimes present in the gravel. (3)
Clay pebbles: LECA (Lightweight Expanded Clay Aggregate) are balls of clay processed at a very high temperature to form into a highly effective growing medium. Clay pebbles are lightweight enough to easily move around when planting and heavy enough to provide good support for small to medium plants. (you may need to support/tie-up tall plants like corn for example) They are also non-degradable, non-toxic, and pH neutral. Clay pebbles are more expensive compared to the other mediums, but because it is reusable, lightweight, and pH neutral; clay pebbles are an investment that will last for many years. (3)
Lava Rock: The naturally created lava rock cools rapidly, which gives no time for the air to escape, effectively trapping it. This trapped air creates a highly porous surface increasing the area of the rock and creating plenty of openings for the nitrifying bacteria to live. Lava rock is light and has a neutral pH, and it won’t affect the balance of your system. Lava rock can be sharp, though, so you will want to use it with caution. (4)
A Bell Siphon is a mechanical device used to regulate the flow of the water easily and efficiently in an aquaponic system. The siphon automatically allows water from the grow bed to be drained into the fish tank. Then the water is pumped from the fish tank into the grow bed. The siphon also maintains a minimum water level and drains any excess water. (4)
Strengths and Weaknesses of a Media-Based System
- Relatively simple and inexpensive.
- Suitable for all kinds of plants from leafy greens to larger fruiting plants.
- Minimal cleaning required.
- For a further breakdown of fish waste, red worms can be added to the gravel bed.
- The media performs a filtering action, preventing debris from returning to the tank.
- The air is present between media particles, supplying oxygen to the roots.
- Suitable for hobby applications, home gardens, and as part of the commercial farm. (5)
- A good-quality medium can be relatively expensive.
- The pore spaces in the medium may get clogged over time, causing anaerobic conditions that are poor for your plants.
- Can require cleaning of the grow bed.
- This style system, by itself, is not usually suitable for commercial purposes due to lower productivity and difficulty in a large-scale implementation.
- The media beds are heavy and need a strong, rigid structure. (5)
Best Plants to Grow in Media Based System
To ensure optimum returns of your aquaponics system it is important to choose the best plant that will thrive in your system. Here are some plants that are best grown in a media based aquaponics system.
The pepper plant is hardy and does not need excessive nutrients to grow. There is a wide variety of peppers to choose from, and all of them grow well in a media-based system. Peppers grow up to three feet tall, so it is important to support the plants as they grow. Peppers will need a warmer environment to grow best. (6)
Turmeric is a very low maintenance plant, known for its many nutritional benefits. Place them on top of your media and the roots will find their way to the nutrient-rich moisture below. Turmeric can be cut in small pieces, and spread on the media bed surface. (7)
Cucumber is a water-based plant, and aquaponics is the best system for them to flourish. Cucumber has a large root structure that thrives in media beds. Because they have vine runners, you can string them into a trellis to make them grow vertically, leaving room for other plants to grow. Cucumbers love sunshine and humidity, so make sure to choose the right place to establish your system where the proper sunlight reaches to cucumber plants.
Tomato is a popular crop that many aquaponics growers like to grow. The media-based system is the best option for growing tomatoes. Before placing the tomato seedling into the media grow bed, it is important to rinse off residual soil that may be attached. Make sure that the plant is covered by at least 2 inches of media, so the stem stays upright and secure.
Other Types of Aquaponics Systems
The raft system also is known as Deep Water Culture or Floating System, and the plants are grown on rafts (polystyrene or foam boards) that float on top of the water in the raft tank. The nutrient-filled water flows continuously from the fish tank through the filtration process, then to the raft tank where the plants are grown and then back to the fish tank. Most often the raft tank is separate from the fish tank
The beneficial bacteria live primarily live in your biofilter or media beds but also in the raft tank and throughout the system benefiting the plants. Plants grow very fast in a raft system can be an easy aquaponics system for the beginner aquaponics gardener to set up and maintain.
Since the development of aquaponics raft systems (DWC) on a commercial scale by Dr. Rakocy at the University of the Virgin Islands. Many commercial aquaponics farms utilize this type of system because it allows the plants to grow faster and yield more crops. The Raft system is best suited for mass production of certain types of vegetables and leafy greens.
Nutrient Film Technique (NFT) System
The Nutrient Film Technique (NFT) is a method of aquaponics in which the plants are grown in a long narrow channel. NFT is both common is hydroponics and aquaponics due to its simple yet effective design. In NFT, a thin film of water flows continuously down each channel, providing the plant roots with water, nutrients, and oxygen. When the water reaches the end of the channel, it is pumped back to the fish tank. NFT use both water and pumps to deliver nutrients to the plants, and the system requires a separate filter to clear the water of solids and biological waste before it’s returned to the fish tank. This system is very efficient in its water use and is primarily used in cultivating greens that have small roots systems. NFT is commonly used in the commercial aquaponic system but can also be used in a hobby system as long as the water is filtered before it is used in NFT channels.
Your choice of aquaponics system depends on you and what you want. We hope this article helps you make a more informed decision on which system is right for you. If you need more information or aquaponic advice, shoot us an email, and we will help you decide what system is best for your needs.