Types of Aquaponics Mediums

Aquaponics is a system that grows plants and fish together to minimize wasted water and the need for fertilizers. The water soluble waste from fish tanks is pumped through grow media in plant beds and provides nutrients to the plants. The plants clean and filter the water as they absorb what they need to grow and return clean water to the fish tank. No soil is required, only the inert and stable grow media of your choice.

Grow media in an aquaponic system has to meet several requirements. The media must provide a solid structure for plants to grow on, but leave enough open space for the roots to grow without clogging up the water flow. It has to provide a large surface area for bacteria growth, oxygen transfer and water retention. The grow media also needs to give the worms used in aquaponics a home and act as a mechanical trap for the solid waste made by the fish. It cannot decompose over time like coir or silica, and it should not change the pH of the water.

Gravel is the cheapest and most readily available grow media used in aquaponic systems. Round gravel between 1/2 and 3/4 of an inch in size is a good aquaponics media, but it has to be rinsed before use and you need to test it to make sure it is not limestone. Limestone raises the pH of water, making the pH of the entire system hard to control. Test gravel for limestone by soaking a sample in vinegar and watching for bubbles, which indicate calcium in the rock. You should also soak it in water and measure the pH after a few days to test for any other pH problems.

The weight of grow media is an important consideration because aquaponic grow beds are 12 inches deep. Leca, or lightweight expanded clay aggregate, is half the weight of gravel and is more porous for better surface area. It is round, so it is easy to handle without hurting your hands, and is the right size at about 3/8 of an inch. Expanded clays also need to be rinsed before use to get rid of all the red dust generated during packaging and shipping. Leca is a popular grow media, but is expensive because it's imported. It is sometimes combined with gravel to reduce cost.

Expanded shale is another aquaponic grow media that has some of the good properties of expanded clay without being as expensive. Its weight is between that of leca and gravel, it is highly porous and though not round, it is polished and smooth so it is easy to handle. Shale is made from ancient lakebed sediments and found in the United States, so the cost is less than that of some expanded clay products. Expanded shale also needs to be rinsed of dust before use.