Fish generally grow best in professionally manufactured round fiberglass tanks designed for aquaculture. Other materials either leech chemicals into the water that can harm the fish, are too difficult to keep clean, or don’t come in round shapes. Building square fish-rearing tanks and trenches from scratch is less than ideal because the corners and flat surfaces make it harder to remove all the solid waste, leading to water quality issues after a few rounds of fish. Deep corners and flat ends also interfere with the water exchange, which should be one full tank or pond’s worth of water per hour. If you must construct the fish-rearing tanks from hand rather than purchase round fiberglass tanks, consider in-ground ponds instead. They are much easier to slope along the sides and edges allowing easier cleaning and better water exchange. Make sure all pond liners and tank materials are food safe unless you are raising strictly ornamental varieties. Many aquarium and pond products are not tested for food production, making them potentially unsafe to use when raising fish to sell as food.

Avoid small plastic tanks, barrels, reinforced plastic tanks like IBC containers, and other reused materials often promoted for backyard and hobby systems. While they may work for small-scale systems, the plastic material is too difficult to clean and sanitize for commercial purposes. The small size of these tanks also makes them almost impossible to scale to the size of a commercial system.

The hydroponic tanks and troughs used for containing vegetables are much easier to design and build from scratch. Regardless of the total number of gallons you need, or the style of growing you choose, you can use materials like lumber and plywood, concrete blocks, cast concrete and even insulated building panels to create affordable, large media or raft beds. Above-ground tanks and trenches are built by creating four sturdy sides that can hold back the weight of the water.  The ground is used as the floor of these structures and a durable pond liner must be installed inside to hold the water.

Because the water flowing through your aquaponics system must be safe for both the crops and fish you grow, any liners you choose for troughs and trenches must be food and fish safe. Just one or the other isn’t enough, especially if you want to qualify for organic certification. The same material restrictions apply to any barrels, buckets and tanks you use in the system that aren’t made from coated fiberglass or metal.

Low-density polyethylene (LDPE) is one of the best materials for a tank or liner in an aquaponics system. It doesn’t release any chemicals or compounds that would be absorbed by the plants or fish, and it’s relatively resistant to UV degradation. High-density polyethylene (HDPE) is the toughest material that is food and fish safe, but it’s also costly and less flexible. For the best liner, look for a product combining layers of both LDPE and HDPE for your aquaponics system.

Always avoid the following pond liner and tank materials for your aquaponics setup:

• PVC, which releases compounds into the water and degrades rapidly when exposed to UV light.
• EDPM sheets for roofing, which may or may not be fish safe but are never food safe.
• Reused or new swimming pool liners, which are treated with compounds that kill the bacteria needed for a healthy aquaponics system.