The Grow Bed
The grow bed component of an aquatic system, is one of the most crucial. Choice of appropriate grow bed is often debated. Debates over what to use, repurpose, build, scavenge or buy for use in backyard aquaponics systems flourish.
Whether Deep Water Culture (DWC), Nutrient Filament Technique (NFT), similar non-media based, or media based, the bulk of grow bed selection criteria and general considerations are universal.
Considerations
A Grow bed can be constructed a variety of materials. Whether purchased new, repurposed from another use, or built, care must be taken to ensure it fulfills certain criteria. At a minimum, the following should be considered. Grow bed design and construction must safely withstand stresses, weight, and pressures involved in containing water, media, plants, and worms. (All of these exert considerable weight and pressure on the structure of the grow bed). So too, must any stands or tables used to hold the grow bed. The material must be waterproof to avoid water leaks. It must be constructed of people, animal, and plant safe materials. It should allow a 1ft depth in grow media. If inside will its location support the weight and space requirements and will there be adequate light or light alternatives. If outside its material composition should be outdoor rated to withstand the elements and UV resistant to avoid breakdown form sunlight.
It’s material(s) must not leak unwanted chemicals into the water, or affect the pH of the water. Materials and construction should, ideally, block out sun, limited unwanted algae growth protecting plant roots in the media from excessive drying and overheating detrimental to plant roots. It should be UV stabilized to ensure that it will not degrade in the sunlight and leach chemicals into the system.
Grow Bed Materials
Commonly used materials in grow bed construction include certain plastics, wood, fiberglass and anything with suitable waterproof liners. Concrete and vermiculite are also be used but care needs to be taken to seal the concrete or vermiculite as they can negatively affect the water chemistry of the system.
The key concept is: Safe Materials….be sure all system components are plant, fish, and human safe.
As list of materials considered suitable to grow bed and tank construction is listed below.
Materials Considered Safe For Grow Bed/Tank Construction
| Polypropylene - labeled PP |
| High Density Polyethylene - labeled HDPE |
| High Impact ABS (Hydroponic Grow Trays) |
| Stainless Steel barrels |
| EPDM or PVC (poly vinyl chloride) pond liner
(make sure its UV resistant and avoid fire retardant material)
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| Fiberglass tanks and grow beds |
| Rigid white PVC pipe and fittings, black flexible PVC tubing, some ABS |
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| DO NOT use Copper – Its toxic to the fish |
Grow Bed Depth and Size
An aquaponic grow bed must be sized appropriately and in complement of the fish tank volume. It must be able to provide adequate mechanical and biological filtration for the nutrient-rich water. For this reason, the grow bed and the fish tank sizes should be considered together to ensure a ratio between the two. A commonly used rule of thumb is a 1-1 ratio between tank and grow bed volume. A 1:3 tank to grow bed ratio will work quite well. Ratios of higher grow bed volumes to tank volume can readily be achieved with adjustments. The ratio and yield can both affected by adjustments to parts of the system. Some areas of possible adjustment would include the number of fish, how much they are fed, type, density, and nutritional requirements of plants, the nutritional content of the feed, volume of fish output, water volume and water flow rate, supplemental filtering and oxygenations techniques.
Appropriate grow bed depth is often a subject of discussion. Though there are always exceptions, there are some general experience guidelines about what has proven to be effective. A media based grow bed consists of three specific layers:
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The surface layer - this layer should be approximately 2 in. (5 cm) in depth. It is above the waterline and should not be wet. The surface layer reduces loss of water through evaporation.
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The root layer - this layer should be approximately 8 in. (20 cm) in depth. This is where roots will be growing and where most plant activity will take place. This is layer is normally regularly flooded and drained.
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The solids layer - this bottom layer should be approximately 2 in. (5 cm) in depth. It is where solid waste will collect and will usually be constantly flooded with water.
These three layer combined yield a recognized suggested grow bed depth of approximately 12 in. (30 cm). It is important to remember that although 12 in depth has been proven itself highly effective, it is not the only depth that can be used. Experiences have demonstrated successful systems with grow bed depths as shallow as 4 in. (10 cm).
There is no required size, type, or construction of grow bed. Think safety first, but don‘t be afraid to be creative.
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