Three main types of aquaponic systems are in use today: Deep Water Culture (DWC), Nutrient Film Technique (NFT), and Media Filled Beds. DWC and NFT systems do not use grow media for plant production, but depend upon nutrient rich water solution. Media filled beds, however, require some suitable material in the grow bed to assist in filtration and facilitate bacterial conversion of waste into plant nutrients. Grow media selection is focused on this last type of system.
Grow Media Functions and Selection Considerations
The grow media in an aquaponic system serves several significant functions. It provides a foundation upon which roots can anchor and plants can grow. This is particularly important ant for larger, fruit bearing or taller plants which have greater support requirements than are offered in DWC and NFT systems. It serves as a natural moderator to changes in temperature. As ambient temperatures swing higher or lower, a grow media buffers the change, maintaining a more stable temperature range for plant roots and the flowing water in the system. It also provides a home for beneficial bacteria and worms together with means of mechanical filtration which facilitates effective conversion of fish waste into plant nutrients.
Because of it importance to an aquaponic system, appropriate media selection is very important. When selecting media several considerations should be made. Media must be pH neutral and must not contain physical or chemical contaminants that will adversely affect the water chemistry or water quality of the system. Media must be properly sized and shaped to ensure proper water drainage and grow bed oxygenation. The media should have a high surface area to facilitate development and sustained levels of beneficial bacteria necessary in waste to nutrient conversion within your system.
Lightweight Expanded Clay Aggregate (LECA)
Lightweight Expanded Clay Aggregate, LECA, is a a type of porous clay pellet that expands when wet. This medium forms a soil-like layer, into which plant roots easily grow and attach. Though somewhat expensive, LECA is a great medium that can be re-used nearly indefinitely. Unlike expanded shale or lava rocks, this pebble like product is round, making it easy on hands and plants during planting. It is far lighter than traditional soil. As with other media, LECA offers a large surface area on which beneficial bacteria can live. It’s neutral pH doesn’t effect water pH. The free draining quality of this medium aids in the necessary oxygenation of roots. Various brands may be available. Always be sure to double check for pH and neutrality, surface area, and draining qualities. Larger sizes help to reduce clogging in the system.
Expanded shale, a sound alternative to LECA, and is less expensive. Expanded shale is created in a process which heats quarried shale to temperatures above 2000oF. The process renders the shale chemically and biologically inert. The heated shale loses its water, which causes the shale to expand. Expanded shale is light weight (much lighter than traditional soil) and irregular in shape. It, too, forms a soil-like layer into which plant roots easily grow and attach. Expanded shale is a great medium that can be re-used nearly indefinitely. Its irregular shape offers a large surface area with “nooks and crannies” offering a great environment on which beneficial bacteria can live. It’s neutral pH doesn’t effect water pH. The free draining quality of this medium aids in the necessary oxygenation of roots. Always be sure to check double check for pH and neutrality, surface area, and draining qualities. Larger sizes help to reduce clogging in the system.
A popular grow medium, Lava rock is a lower cost alternative to expanded clay or expanded shale. It is very popular in many areas due to its availability and cost (approximately 75% less expensive). This naturally occurring alternative LECA and expanded shale, is lightweight, porous and has many of the same properties. As is the case with expanded shale, this irregularly shaped medium makes it a bit more difficult to work with than clay pebbles. Because it is naturally occurring it is important to to ensure that there are no impurities or chemicals present.
River Gravel or Pea gravel
This naturally occurring medium is much heavier and at somewhat more difficult to work with than other medium. It is, however, far less expensive by comparison and is more readily available. River or Pea gravel doesn’t have as much surface area as expanded clay or shale and doesn‘t hold water well. This reduces its effectiveness in bio-filtration. Mineral composition may affect pH or impurity content, negating the chemical suitability of particular pebbles (pH . Taller, more top heavy plants, such as corn, are better supported by the heavier densities of this medium. This medium might be a boon to those with tighter budgets. Gravel, particularly, should be tested for chemical suitability before it is included in your aquaponics system. A simple, well known and often used quick test is to take several random samples and add vinegar. If the mixture of pebble(s) and vinegar reacts, the pebbles should not be used.
Perlite / Vermiculite / Sand / Coir / Glass Beads
A number of other media can be used in Aqualon systems, including: perlite; vermiculite; sand; coir; glass beads. All can and have been successfully used as either a complete grow bed media - or in addition to another media, such as expanded clay or shale. Their physical and chemical suitability should be considered before they are included in your system. The relatively small sizes of perlite, vermiculite, sand, and coir may impede water drainage and oxygenation, or introduce or increase clogging problems. Coir, a natural cocoanut product, may discolor water and, being an organic medium, introduce unwanted organisms. PH neutrality and leached impurities must also be checked.
Wash Grow Bed Media Before Use?
Though some question the need to wash media before use, we recommend it. It is time consuming and labor intensive and will increase initial water usage. However, water quality is improved from the start because it washes away debris, insects, and surface impurities at the outset. Washing may reduce ongoing cleaning and maintenance. It will likely also increase the life of your pump and any additional filtering equipment as well. The choice is yours to make.