Water quality in aquaponics
Working within the tolerance range for each organism
As discussed in Chapter 2, aquaponics is primarily about balancing an ecosystem of three groups of organisms: fish, plants and bacteria (Figure 3.2). Each organism in an aquaponic unit has a specific tolerance range for each parameter of water quality (Table 3.1). The tolerance ranges are relatively similar for all three organisms, but there is need for compromise and therefore some organisms will not be functioning at their optimum level.
· Food and Agriculture Organization of the United NationsWater testing
In order to maintain good water quality in aquaponic units, it is recommended to perform water tests once per week to make sure all the parameters are within the optimum levels. However, mature and seasoned aquaponic units will have consistent water chemistry and do not need to be tested as often. In these cases water testing is only needed if a problem is suspected. In addition, daily health monitoring of the fish and the plants growing in the unit will indicate if something is wrong, although this method is not a substitution for water testing.
· 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 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 NationsOther major components of water quality: algae and parasites
Photosynthetic activity of algae Photosynthetic growth and activity by algae in aquaponic units affect the water quality parameters of pH, DO, and nitrogen levels. Algae are a class of photosynthetic organisms that are similar to plants, and they will readily grow in any body of water that is rich in nutrients and exposed to sunlight. Some algae are microscopic, single-celled organisms called phytoplankton, which can colour the water green (Figure 3.
· Food and Agriculture Organization of the United NationsManipulating ph
There are simple methods to manipulate the pH in aquaponic units. In regions with limestone or chalk bedrock, the natural water is often hard with high pH. Therefore, periodic acid additions may be necessary to lower the pH. In regions with volcanic bedrock, the natural water will often be soft, with very low alkalinity, indicating a need to periodically add a base or a carbonate buffer to the water to counteract the natural acidification of the aquaponic unit.
· Food and Agriculture Organization of the United Nations