Which Fish Tank?

Aquaponics requires containers (tanks) for the water for the fish, shrimp or other aquatic beings that will provide nutrients, as well as containers for the plants. This article focuses on the tanks for the aquatic beings who supply the nutrients. 

Tank Size: Almost any size tank can be used but the larger the tank the more potential for nutrients and the more plants which can be grown. A well-stocked 100 gallon tank for fish or other aquatic beings can provide enough nutrients to grow a considerable volume of plants. One way to determine size if to first decide what you want to grow and how much of it.

A general guideline for estimating production is 0.45 kg (1 pound) of fish per 19-38 liters (5-10 gallons) of water, with the fish waste supporting about 0.09-0.19 square meters (1-2 square feet) of plant growing area per 3.8 liters (1 gallon) of fish tank volume. This assumes a fully cycled tank with adequate filtration and aeration and the addition of nutrients that may be deficient in the fish waste. However, there is a high degree of variability in type of fish, water chemistry, temperature, feeding and the plants grown. 

So, as a rough example: a 378-liter (100-gallon) fish tank might support 4.5-9 kg (10-20 pounds) of fish and sustain 9.3-18.6 square meters (100-200 square feet) of grow bed, potentially producing 23-45 kg (50-100 pounds) of leafy greens annually, assuming optimal conditions.

Tank Material Toxicity: One of the first considerations for tank material is toxicity. One of the big mistakes that many people make in aquaponics is using tanks made from materials that leach toxic chemicals and/or heavy metals. 

Plastic storage tubs are inexpensive and commonly used by some but are generally made from non-food grade high-density polyethylene (HDPE) plastic, which leach various toxins into the water. Simply washing or soaking them isn't sufficient. The thinner tubs can crack under the pressure of water or just from age. Filtering the water vigorously with carbon and ion-exchange resins can reduce the toxicity, but the ion-exchange resin can also remove important nutrients. Best to avoid storage tubs altogether. 

IBC totes hold 1,000 liters (264 gallons) and are used for shipping a wide range of liquids and can make a cost effective tank but are also made from HDPE and must be not just be food-grade but also thoroughly washed (steam-cleaning is best). It is best to fill them with water and let them sit for a month, drain and rinse thoroughly before putting into production. For aquaponics operations most people cut the top off and use the top for a plant tray. The tanks are rather thin and require the metal frame they come in for support. Aquaponics.pro will be selling IBC totes suitable for aquaponics. 

20 or 23 liter food-grade plastic buckets can be suitable for small fish, crayfish, shrimp, snails or other small aquatic beings but only if the bucket is aerated and the water filtered. We have used food grade buckets previously used in a wine-making kit. However, these are generally white in color and allow in too much light which encourages the growth of algae. You can cover the outside of the buckets to reduce light penetration. Some companies do make black food-grade buckets. 

Aquariums are suitable for smaller tanks and the least toxic option. DIY glass tanks should be made only with aquarium grade silicone sealant. Large glass tanks can be made with used glass but tempered glass can't be cut without difficulty. Acrylic tanks are OK, lighter in weight but more expensive and easier to scratch. 

Pond liners sold specifically for ornamental or commercial ponds containing fish are often made from EPDM (ethylene propylene diene monomer), RPE (reinforced polyethylene), or certain HDPE (high-density polyethylene) and are generally considered safe but should washed thoroughly before use. Pond liners sold for general agricultural use and environmental remediation may not be so safe. Plastic sheeting for construction or general purpose should not be used. 

Fiberglass tanks are only safe if they are made by a reputable manufacturer specifically for aquaculture or the food industry. Otherwise they can leach toxic chemicals. If you are going to build your own fiberglass tank be sure that you only use resin that is free from fire retardants and don't use fillers. Fiberglass tanks must be fully cured and not have any odor. Odor means chemical toxins. In Nova Scotia, suitable fiberglass tanks are extremely expensive new but you might be able to pick up some used that are in serviceable condition. 

Galvanized metal stock tanks can be an option but do leach zinc into the water. The zinc can be reduced through frequent water changes and a strong cation ion-exchange resin such as Amberlite IR-120 or Purolite C100. One should never use water that is high in copper or a copper based medication with a galvanized tank as it will cause substantial zinc leaching. 

Wooden tanks can be an affordable option. One can build a tank from wood and line it with a suitable pond-liner, coat the inside with a food-grade coating or used glass. If using plywood be sure that it can support the weight and is smooth on the inside. A good pond liner may be the least expensive and most durable lining option. A wooden tank could be unlined if built properly with aged wood but even the tightest seam may leak and encourage the growth of mold. 

Concrete tanks are a viable option for large-scale long-term operations but can require a considerable investment and if not sealed can make water more alkaline. 

Plastic rain barrels, anything from PVC or ABS plastic should generally be considered unsafe. However, there are food-grade plastic drums that can be used, but they may lack sufficient surface area.