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.
TABLE 3.1
General water quality tolerances for fish (warm- or cold-water), hydroponic plants and nitrifying bacteria
| Organism type | Temp (°C) | pH | Ammonia (mg/litre) | Nitrite (mg/litre) | Nitrate (mg/litre) | DO(mg/litre) |
| Warm water fish | 22–32 | 6–8.5 | < 3 | < 1 | < 400 | 4–6 |
| Cold water fish | 10–18 | 6–8.5 | < 1 | < 0.1 | < 400 | 6–8 |
| Plants | 16–30 | 5.5–7.5 | < 30 | < 1 | - | > 3 |
| Bacteria | 14–34 | 6–8.5 | < 3 | < 1 | - | 4–8 |
Table 3.2 illustrates the ideal compromise for aquaponics that is needed for the key water quality parameters. The two most important parameters to balance are pH and temperature. It is recommended that the pH be maintained at a compromised level of 6-7, or slightly acidic.
TABLE 3.2
Ideal parameters for aquaponics as a compromise between all three organisms
| Temp (°C) | pH | Ammonia (mg/litre) | Nitrite (mg/litre) | Nitrate (mg/litre) | DO (mg/litre) | |
| Aquaponics | 18–30 | 6–7 | < 1 | < 1 | 5–150 | > 5 |
The general temperature range is 18-30 °C, and should be managed in regard to the target fish or plant species cultivated; bacteria thrive throughout this range. It is important to choose appropriate pairings of fish and plant species that match well with the environmental conditions. Chapter 7 and Appendix 1 describe the optimal growing temperatures of common fish and plants.
The overall goal is to maintain a healthy ecosystem with water quality parameters that satisfy the requirements for growing fish, vegetables and bacteria simultaneously. There are occasions when the water quality will need to be actively manipulated to meet these criteria and keep the system functioning properly.
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.