Aquaponics is a relatively new practice and various types of aquaponics plans are still developing. So far 2 primary designs have evolved. First, there is the raft system where the plants are grown on polystyrene boards that float on top of the water with continuous water flow. Secondly, there is the media bed system, which uses gravel, lava rock or another filtration substance for the plant bed. In the media bed system, the pump cycles on and off, alternatively flooding the plant bed and then utilizing gravity to drain the water back into the fish tank. The arrangement and size of the system is ultimatley by the type and scale of food production that is required, the space available and the expertise of the practitioner.
Aquaponics Plans Based on Food Production
In most designs, the raft system utilizes three components, typically fish tanks, plant beds and filtration mechanisms. The relative size of these fish and plant components can be as simple as maintaining a 1 to 1 ratio of water volume, but for efficiency, research has shown that the surface area of the plant beds can be as high as 7 times the surface area of the fish tanks and carry 75% of the water volume. One of the advantages of the raft system is that the high volume of water it can carry in the multiple tanks provides a buffer that enables a high density of fish to be safely stocked and subsequently harvested at about .5 lbs per gallon while safely maintaining water quality. Most commercial aquaponics operations use this method. The media system does not need the filtration tank and can get by with only 2 components. The ratio between components is typically designed at 1 to 1 surface area ratio, but can go as high as more 2 or 3 to 1. Due to the use of filter media instead of water in the grow beds, the stocking ratio for the fish is also less than the raft system at .2 -.3 lbs per gallon. The media bed can also provide sufficient filtration eliminating the need for the third component. The media system is generally simpler and less expensive to set up and operate and is used by most hobbyists but in terms of production, it is much less efficient than the raft system. Using these guidelines for planning purposes, the size of an aquaponics system can be calculated for various levels of desired food production.
Aquaponics Plans Base on Fish Yield
The most popular fish for both raft and media bed aquaponics systems are tilapia. Tilapia can typically grow from fingerlings to 1 lb in 5 to 6 months, so 2 harvests of eatable size fish can be produced per year. Using these planning numbers, a 250 gallon fish tank with a harvest ratio of .3 lbs per gallon can produce about 150 lbs of fish per year. A 1000 gallon tank or four 250 gallon tanks can produce 600 lbs of fish.
Aquaponics Plans Based on Produce Yield
The aquaponics method, the type of fish, the density of the population, the feeding rate, and water flow rate must all be considered when determining the actual size of the plant bed that can be supported by various size fish tanks but a general rule of thumb is 1 to 2 ft of growing area for every 10 gallons of water. Using this ratio a 250 gallon tank can support a grow bed of up to 50 sq ft. A plant bed this size can produce around 300 lbs of tomatoes, 600 lbs of lettuce or 100 lbs of eggplant per year.
Again many other factors effect actual production, but when devising your aquaponics plans these factors and ratios can be used to provide a rough sense for the yield of produce and fish that can be expected in a given space.