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Understanding water chemistry in aquaponics is essential to providing optimal growth conditions for the fish, plants, and bacteria. By culturing fish in a recirculating system, all the essential elements for survival—such as temperature, oxygen, pH, and water clarity—need to be provided. Like all organisms, those cultured in aquaponic systems have optimum ranges for growth and survival. While there is overlap between optimum water quality ranges for each organism, a compromise must be made in many aspects of production (Table 6).
Table 6: Recommended water quality parameters for aquaponics*.
| Organism | Temperature (°C) | pH | Ammonia (mg/L) | Nitrite (mg/L) | Nitrate (mg/L) | DO (mg/L) |
|---|
| 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 | < 250 | > 3 |
|---|
| Bacteria | 14 - 34 | 6 - 8.5 | < 3 | < 1 | - | 4 - 8 |
|---|
| Compromise for Aquaponics | 18 - 30 | 6 - 7 | < 1 | < 1 | < 150 | 5 - 8 |
|---|
The five most important water chemistry parameters to consider for aquaponics are dissolved oxygen, temperature, pH, total ammonia nitrogen, and alkalinity.
Oxygen is required at high levels by fish, plants, and bacteria. Oxygen content is quantified by the dissolved oxygen (DO) in water and is expressed as milligrams per liter (mg/L) (Somerville et al. 2014). The intensive nature of aquaponic systems requires oxygen supplementation. Oxygen can enter the system by agitation at the surface or by diffusers in the water column. Fish stocking density, number and type of plants, amount of organic solids, biological oxygen demand, and temperature are all factors that determine how much DO is needed (Rackocy et al. 2006, Wurts and Durborow 1992). DO and temperature have an important relationship. Oxygen is more soluble in cold water than it is in warm water, meaning that cold water can retain higher levels of dissolved oxygen than warm water. This is particularly important for producers raising warm water fish or operating in areas that experience high year-round or seasonal temperatures. It is recommended that dissolved oxygen be maintained between 5-8 mg/L. DO is difficult to measure, as meters can be expensive or hard to find. In this case, producers can purchase DO aquarium test kits or contact local Extension or universities for assistance.