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Unwanted bacteria
Sulphate reducing bacteria Nitrifying and mineralizing bacteria are useful to aquaponic systems, but some other types of bacteria are harmful. One of these harmful groups of bacteria is the sulphate- reducing group. These bacteria are found in anaerobic conditions (no oxygen), where they obtain energy through a redox reaction using sulphur. The problem is that this process produces hydrogen sulphide (H2S), which is extremely toxic to fish. These bacteria are common, found in lakes, saltmarshes and estuaries around the world, and are part of the natural sulphur cycle.
· Food and Agriculture Organization of the United NationsTroubleshooting for common problems in aquaponic systems
Table 8.4 lists the most common problems when running an aquaponic unit. If anything appears out of the ordinary, immediately check that the water pump and air pumps are functioning. Low DO levels, including accidental leaks, are the number one killer in aquaponic units. As long as the water is flowing, the system is not in an emergency phase and the problem can be addressed systematically and calmly. The first step is always to conduct a full water quality analysis.
· Food and Agriculture Organization of the United NationsThe media bed technique
Media-filled bed units are the most popular design for small-scale aquaponics. This method is strongly recommended for most developing regions. These designs are efficient with space, have a relatively low initial cost and are suitable for beginners because of their simplicity. In media bed units, the medium is used to support the roots of the plants and also the same medium functions as a filter, both mechanical and biological. This double function is the main reason why media bed units are the simplest; the following sections demonstrate how NFT and DWC methods both require isolated and more complicated components for filtration.
· Food and Agriculture Organization of the United NationsThe five most important water quality parameters
Oxygen Oxygen is essential for all three organisms involved in aquaponics; plants, fish and nitrifying bacteria all need oxygen to live. The DO level describes the amount of molecular oxygen within the water, and it is measured in milligrams per litre. It is the water quality parameter that has the most immediate and drastic effect on aquaponics. Indeed, fish may die within hours when exposed to low DO within the fish tanks.
· Food and Agriculture Organization of the United NationsThe biofilter
Nitrifying bacteria are vital for the overall functioning of an aquaponic unit. Chapter 4 describes how the biofilter component for each aquaponic method works, and Chapter 5 describes the different bacteria groups that operate in an aquaponic unit. Two major groups of nitrifying bacteria are involved in the nitrification process: 1) the ammonia-oxidizing bacteria (AOB), and 2) the nitrite-oxidizing bacteria (NOB) (Figure 2.6). They metabolize the ammonia in the following order:
· Food and Agriculture Organization of the United NationsSystem cycling and starting a biofilter colony
System cycling is a term that describes the initial process of building a bacterial colony when first starting any RAS, including an aquaponic unit. Under normal circumstances, this takes 3-5 weeks; cycling is a slow process that requires patience. Overall, the process involves constantly introducing an ammonia source into the aquaponic unit, feeding the new bacterial colony, and creating a biofilter. The progress is measured by monitoring the nitrogen levels. Generally, cycling takes place once an aquaponic system is built, but it is possible to give the biofilter a head start when creating a new aquaponic system.
· Food and Agriculture Organization of the United NationsSustainable, local alternatives for aquaponic inputs
Organic plant fertilizers Chapter 6 discussed how even balanced aquaponic systems can experience nutrient deficiencies. Although fish food pellets are a whole feed for fish, they do not necessarily have the right quantities of nutrients for plants. Generally, fish feeds have low iron, calcium and potassium values. Plant deficiencies can also arise in suboptimal growing conditions, such as cold weather and winter months. Thus, supplementary plant fertilizers may be necessary, particularly when growing fruiting vegetables or those with high nutrient demands.
· Food and Agriculture Organization of the United NationsSources of aquaponic water
On average, an aquaponic system uses 1-3 percent of its total water volume per day, depending on the type of plants being grown and the location. Water is used by the plants through natural evapotranspiration as well as being retained within the plant tissues. Additional water is lost from direct evaporation and splashing. As such, the unit will need to be replenished periodically. The water source used will have an impact on the water chemistry of the unit.
· Food and Agriculture Organization of the United NationsSite selection
Site selection is an important aspect that must be considered before installing an aquaponic unit. This section generally refers to aquaponic units built outdoors without a greenhouse. However, there are brief comments about greenhouses and shading net structures for larger units. It is important to remember that some of the system’s components, especially the water and stone media, are heavy and hard to move, so it is worth building the system in its final location.
· Food and Agriculture Organization of the United NationsSecuring water levels for a small-scale unit
One of the most common disasters for small-scale or commercial aquaponic units is a loss-of-water event where all of the water drains from the unit. This can be catastrophic and kill all of the fish, destroying the system. There are several common ways for this to happen, including electricity cuts, blocked pipes, drains left open, forgetting to add new water or disruption of water flow by animals. All of these issues can be fatal for fish in a matter of hours if problems are not dealt with immediately.
· Food and Agriculture Organization of the United Nations