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This chapter describes the basic concepts of managing the water within an aquaponic system. The chapter begins by setting the framework and comments on the importance of good water quality for successful aquaponic food production. Following this, the major water quality parameters are discussed in detail. Management and manipulation of some of the parameters are discussed, especially in regard to sourcing water when replenishing an aquaponic unit.
Water is the life-blood of an aquaponic system. It is the medium through which all essential macro- and micronutrients are transported to the plants, and the medium through which the fish receive oxygen. Thus, it is one of the most important topics to understand. Five key water quality parameters are discussed: dissolved oxygen (DO), pH, temperature, total nitrogen, and water alkalinity. Each parameter has an impact on all three organisms in the unit (fish, plants and bacteria), and understanding the effects of each parameter is crucial. Although some aspects of the knowledge on water quality and water chemistry needed for aquaponics seem complicated, the actual management is relatively simple with the help of simple test kits (Figure 3.1). Water testing is essential to keeping good water quality in the system.
Water is the life-blood of an aquaponic system. It is the medium through which plants receive their nutrients and the fish receive their oxygen. It is very important to understand water quality and basic water chemistry in order to properly manage aquaponics.
There are five key water quality parameters for aquaponics: dissolved oxygen (DO), pH, water temperature, total nitrogen concentrations and hardness (KH). Knowing the effects of each parameter on fish, plants and bacteria is crucial.
Compromises are made for some water quality parameters to meet the needs of each organism in aquaponics.
The target ranges for each parameter are as follows:
|Water temperature||18-30 °C|
There are simple ways to adjust pH. Bases, and less often acids, can be added in small amounts to the water in order to increase or lower the pH, respectively. Acids and bases should always be added slowly, deliberately and carefully. Rainwater can be alternatively used to let the system naturally lower the pH through nitrifying bacteria consuming the system's alkalinity. Calcium carbonate from limestone, seashells or egg shells increases KH and buffers pH against the natural acidification.
Some aspects of the water quality and water chemistry knowledge needed for aquaponics can be complicated, in particular the relationship between pH and hardness, but basic water tests are used to simplify water quality management.
Water testing is essential to maintaining good water quality in the system. Test and record the following water quality parameters each week: pH, water temperature, nitrate and carbonate hardness. Ammonia and nitrite tests should be used especially at system start-up and if abnormal fish mortality raises toxicity concerns.
Source: Food and Agriculture Organization of the United Nations, 2014, Christopher Somerville, Moti Cohen, Edoardo Pantanella, Austin Stankus and Alessandro Lovatelli, Small-scale aquaponic food production, http://www.fao.org/3/a-i4021e.pdf. Reproduced with permission.