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How Aquaponics Works

Aquaponics Basics
It might seem strange, but plants can thrive without soil.
It might seem strange, but plants can thrive without soil.
Shannon Fagan/Getty Images

Cultivating plants and fish through aquaponics is both easy on the environment and easy on finances. Aquaponic systems don't use any chemicals, and they require about 10 percent of the water used in regular farming. The systems are closed -- that is, once they've been filled with water, only a small amount is introduced into the system thereafter to replace evaporated water. But how can a water-based system use less water than conventional farming?

The answer is the continual reuse and recycling of water through naturally occurring biological processes. Basically, the waste from fish produces natural bacteria that converts waste like ammonia into nitrate. This nitrate is then absorbed by plants as a source of nutrients. The basic principle of aquaponics is to put waste to use.

Let's take a look at the step-by-step process:

  • Fish living in aquaponic tanks excrete waste and respirate ammonia into water. Ammonia is toxic to fish in high concentrations, so it has to be removed from the fish tanks for fish to remain healthy.
  • Ammonia-laden water is processed to harvest helpful types of bacteria such as Nitrosomonas and Nitrobacter. Nitrosomonas turns ammonia into nitrite, while nitrobacter converts into nitrate. Both of these nitrates can be used as plant fertilizer.
  • Nitrate-rich water is introduced to the hydroponically grown plants (plants grown without soil). These plants are placed in beds that sit on tubs filled with water, and the water is enhanced by the nitrate harvested from the fish waste. The plants' bare roots hang through holes in the beds and dangle in the nutrient-laden water.
  • The roots of the plants absorb nitrates, which act as nutrient-rich plant food. These nitrates, which come from fish manure, algae and decomposing fish feed, would otherwise build up to toxic levels in the fish tanks and kill the fish. But instead, they serve as fertilizer for the plants.
  • The hydroponic plants' roots function as a biofilter -- they strip ammonia, nitrates, nitrites and phosphorus from the water. Then, that clean water is circulated back into the fish tanks.

Because fish waste is used as fertilizer, there's no need for chemical fertilizers. The money and energy it would take to put those chemicals to work is saved. In fact, the only conventional farming method that's used to operate an aquaponics system is feeding the fish.

Now you know how aquaponics works on a biochemical level. But which kinds of fish are best for these systems? And which plants thrive in them? Let's find out.