Many aquaponic systems, from DIY home-builds to commercial facilities, use plastic containers or soft-lined grow beds. This is because plastic containers, such as recycled Low-Density Polyethylene (LDPE) Intermediate Bulk Containers (IBCs) or High-Density Polyethylene (HDPE) Molded Tanks are relatively inexpensive, readily available, and easy to hand, drill, and plumb. When looking to construct something truly unique, or customized to fit a particular space, plastic containers and soft-liners have limitations related to shape and structural integrity.
Although plastic is an excellent material to form round tanks, structural integrity is compromised when plastic is used to form rectangular containers. This is because the outward force of water in a cylinder is distributed evenly in all directions, while the uneven forces in a rectangular container will cause warping and bowing over time. This is why IBC totes require a structural metal cage to maintain their shape, and why the metal cage should remain in place if sectioning an IBC into grow beds.
Advantages of Fiberglass
As round grow-beds would not be user-friendly or an economic use of space, rectangular grow beds are often constructed from a stronger material, such as metal square-tube, masonry block, or wood, which is then fitted with a water-tight HDPE liner, such as reinforced plastic Dura Skrim or woven PolyMax. While these materials are great for constructing inexpensive beds, creating more dynamic shapes with curves or bends is difficult, and often renders beds that are aesthetically displeasing.
Although fiberglass beds are more expensive than the above materials, fiberglass allows for beds to be constructed in any shape or configuration without concerns of structural integrity or warping over time. Additionally, epoxy-painted fiberglass beds, such as the white beds commonly used in our ‘show-case’ systems, maintain a clean aesthetic that fits well with acrylic fish tanks and steel accents.
On larger systems like the implementation at Commonwealth Charter Academy (CCA), where the fiberglass beds were custom-built to form the letters ‘CCA’, the beds were shipped in multiple pieces, and had to be bolted together, then seamed with filler, fiberglass, and resin.
For the installation that we designed and constructed for Intag at Cedar Cliff High School, we opted to have the grow beds molded and shipped as whole pieces. Although this saved on installation time, and kept the lines of the curves clean of seams and bolts, it made getting the beds into the interior room of the school a fun challenge.
Working with Fiberglass Beds
If you opt to work with fiberglass beds, particular care should be taken when cutting in through-ports, such as uniseals or bulkheads fittings. When drilling plastic containers with a hole-saw it is advised to set the drill in reverse, so that the hole-saw slowly cuts/melts its way through the plastic container. Additionally, a duller hole-saw can be used to cut plastic containers, and will render a clean, smooth edge to the hole. Any burs or roughness can be easily cleaned-up by gently scraping with a blade, or flashing the plastic quickly with a lighter or small torch.
When using a hole-saw for cutting a through-port into a fiberglass bed, a sharp hole-saw should be used, and time should be taken to slowly cut through the various layers of fiberglass, as this will decrease the risk of chipping the outer, often painted or gel-coated surface of the bed. Furthermore, the hole should be drilled from both sides in order to avoid blow-out of the outer layer of the back of the fiberglass bed. Starting on the outside of the fiberglass bed, begin drilling the hole until the pilot bit of the hole-saw has clearly cut through the bed, and the hole-saw is roughly half-way through the wall of the bed.
Moving to the inside of the bed, ensure that the pilot bit is centered properly in the pilot hole that is on the inside of the bed, proceed to drill the rest of the way through the fiberglass side-wall from the inside of the bed. This will result in a clean hole, minimizing the risk of blow-out on either side of the bed. Aside from being unsightly, blow-out can allow direct contact of water to the uncoated fiberglass. On containers that have a wood or foam core, this can lead to delamination over time.
Even when Drilling fiberglass from both sides, fracturing can occur along the inside of the cut, leaving a sharp ridge along parts of the inside edge of hole. If you are using a rubber uniseal fitting, this edge can damage the body of the uniseal, leading to an eventual leak. For this reason, it is advised that the hole be gently sanded smooth before inserting the uniseal.
As shown here, one of the uniseals on this system was experiencing a slow drip. After digging out the media-bed to access the plumbing, the uniseal and hole was inspected, and it was found that a sharp ridge in the fiberglass has worn a cut into the uniseal. The hole was cleaned up, gently sanded smooth, and a new uniseal was installed.