When designing your aquaponics system, it is crucial to consider the size of your fish tank early on, as it determines the overall size and flexibility of your system. If you plan on creating a small desktop system using an aquarium, the size of the fish you can accommodate will be limited to those that can comfortably live in the size aquarium you have. However, if you aim to raise larger edible fish, it is essential to choose a tank that is constructed with sturdy, food-grade, or food-safe materials. Additionally, it is important to select a tank that is at least 18 inches deep (457mm) and has a minimum water capacity of 50 gallons (189 Liters). A tank of this size or larger is required to cultivate fish of a size typically found on a dinner plate, measuring 12 inches in length and weighing approximately 1 ½ pounds (300mm and 680g).
EPDM pond liner is used to line any structure that meets the appropriate dimensions in order to create aquaponics fish tanks.
From recycled barrels to recycled bathtubs, stock tanks, and IBC tanks, you can utilize a variety of options.
It is important to think carefully about where you will place your fish tank since it will be hard to move once it is filled. Ideally, the tank should be placed indoors or outdoors in a shaded area. Sunlight is not necessary for fish to thrive and it could cause issues such as excessive heat and algae growth. Additionally, ensure that the surface on which the tank is placed is sturdy enough to support the weight of the filled tank. Considering that water weighs 8.3 pounds per gallon, the weight of the tank may surpass the structural limits of the chosen surface.
To ensure debris, children, and pets do not fall into your tank, it is advisable to cover it partially at the location of your choice. By doing so, you will also decrease the amount of light that reaches the tank, which aids in maintaining the tank’s temperature and minimizing algae growth.
Grow bed
The maximum size of your grow bed is determined by the volume of your fish tank. This is because the plants need fish waste in order to thrive. The larger the grow bed, and therefore the more plants, the more fish waste is needed. It’s simple – you need enough fish to support your plants. Generally, the recommended ratio of grow bed to fish tank is 1:1. This means that the volume of the fish tank should be approximately equal to the volume of the grow bed. Another way to think of this ratio is aiming for 6 gallons (22 liters) of fish tank volume per cubic foot of grow bed. For instance, a 50-gallon (189 liters) tank would be able to support 6 to 8 cubic feet of grow bed. You can extend this rule of thumb to a ratio of 2:1 (twice the fish tank volume to grow bed volume), but make sure to reduce the stocking density of your fish tank accordingly. This will decrease your ability to filter the fish tank water with the grow bed plants.
It is not recommended to use metal containers, including galvanized metal, for the grow bed or fish tank due to the possibility of rapid corrosion which can disrupt the system’s balance by decreasing the tank’s pH level. Additionally, metal containers have the potential to release unwanted chemicals into the system, with copper and zinc being especially harmful for fish.
Sizing a System for Deep Water Production
The most popular form of commercial aquaponics in warm climates is Deep Water Culture (DWC), which is also commonly known as raft production. This system requires a large amount of water for the hydroponics part of the equipment. Therefore, most systems that use rafts have a water ratio of approximately seven times more for plants than for fish. In the University of Virgin Islands system, the original commercial raft aquaponics design consists of four 2,000-gallon fish tanks paired with four 3,000-gallon troughs. Additionally, there are added sump and settling tanks that amount to a little over 2,500 gallons. This results in a 22,500-gallon system that can produce up to 4.75 metric tons of tilapia and five metric tons of basil per year. Raft systems such as the UVI design commonly have higher fish stocking rates and additional tanks and filters to manage the significant load of dissolved solids.
To maintain the appropriate balance of nutrients without overloading the filters or causing nitrogen deficiency in plants, it is recommended to have a feed ratio between 60 to 100 grams per square meter of growing area per day in DWC. This wide range allows for the diverse requirements of different stocked fish. If aiming to promote rapid growth in tilapia, a daily feed ratio of 75 grams/m2/day can be considered, leading to the following potential outcomes:
- Average daily feed rates of 150 grams per 100 tilapia
- Stocking rate of 2 lbs. of mature fish weight per 1 cubic foot of rearing space
- 1,000 lbs. of fish in two 2,000-gallon tanks
- 1,500 grams of feed per day
- 1,500 grams/day divided by 75 grams = 20 square meters of growing space required
Although the quantity of 1,000 fish may seem significant, it can only sustain a relatively small growing area at such a high stocking rate. If your objective is to have a growing area of 300 square meters and a daily feed ratio of 100 grams/m2/day, you will require approximately 20,000 pounds of tilapia to maintain that ratio. Considering that the ratio of pounds of mature fish to cubic feet of water is 2:1, you will need more than 75,000 gallons of water to accommodate all those fish. While certain deep water culture systems operate with daily feed ratios as low as 10-20 grams/m2/day, these rates result in such slow growth that they are rarely feasible for commercial production. It is recommended to plan for a minimum ratio of 50 grams/m2/day for raft production to ensure profitability.
Sizing Aquaponics for a Nutrient Film Technique Installation
Due to the lower amount of water needed to flush the plant roots in the pipes of an NFT system, the recommended daily feed ratios are only about 25% of what is recommended for DWC/raft culture. If the stocking density is too high or the tanks are too large, excess feed entering the system can cause nutrient overloading and harm or kill the plants. Assuming proper filtration and settling tank additions in both the fish and plant tanks, NFT systems should be fed at a rate of 15-25 grams/m2/day. Therefore, if a daily feed ratio of 20 grams/m2/day is chosen:
- Average daily feed rates of 150 grams per 100 tilapia
- Stocking rates of 1 lb. of mature fish weight per 1 cubic foot of rearing space
- 500 lbs. of fish in two 2,000-gallon tanks
- 750 grams of feed per day
- 750 grams/day divided by 20 grams = 37.5 m2 of growing space required
If you are considering profitability, raft culture is likely to yield higher profits than NFT growing methods due to its lower stocking rates and daily feed ratios. This may result in relatively small fish harvests compared to DWC systems, but it can save on fish feed supplies and filtration units. However, if your market primarily values plants over fish and you only intend to use fish as a fertilizer source, then raft culture may not be as profitable.
Sizing for Pond-based and In-ground Systems
When using pond-based aquaponics for DWC/raft production, you can use the same numbers and feed ratios as you would for above-ground troughs. However, if you choose to use in-ground media beds and in-ground ponds for fish production, you will need a slightly different sizing plan. This plan can be determined by using a calculator to calculate the size of the system based on the desired size of the bed and whether it will be used as a biofilter or have additional filtration. It is important to adjust the calculations based on the protein level of the feed since there will be fewer filters and tanks to capture solid waste. While there is no simple formula to provide due to the various variables involved, you can find numerous reliable and free media bed sizing calculators online.
