Water Quality Parameters
6.7 Corrective Measures
Low dissolved oxygen (below 5 mg/L): increase aeration, reduce feeding until corrected Low pH (below 6.0): add base (calcium hydroxide, calcium carbonate, potassium hydroxide or potassium carbonate), reduce feeding until corrected High ammonia (above 1 mg/L TAN): reduce feeding until corrected, perform 20% water exchange, check for accumulated solids, increase biological filtration High nitrite (above 0.5 mg/L): reduce feeding until corrected, perform 20% water exchange, increase biological filtration Consistently high nitrate: reduce fish biomass or feeding rate, add more plant biomass
· Kentucky State University6.6 Cycling the System
Cycling refers to the process of establishing the biological filter. This can take between six to eight weeks (Figure 17). Nitrifying bacteria are found naturally in the environment, so the process begins by adding a source of ammonia. This can be accomplished through adding fish, fish food, or water from a well-established system, or a combination of these. One of the most common mistakes when using fish to cycle a system is adding too many fish initially.
· Kentucky State University6.5 Alkalinity
Alkalinity is an often-overlooked aspect of water quality but is essential in maintaining a stable system. Alkalinity is a measure of water’s ability to buffer, or resist, changes in pH (Wurts and Durborow 1992). The most common forms of alkalinity are carbonates (CO~3~-) and bicarbonates (HCO~3~-). These carbonates bind to free H^+^ ions, a result of nitrification, preventing a drop in pH. Water with low alkalinity and a steady rate of nitrification experience wide swings in pH, which can be detrimental to the health of fish, plants, and bacteria.
· Kentucky State University6.4 Total Ammonia-Nitrogen
Nitrogen enters the aquaponic system as crude protein in the fish feed. Approximately 30% of protein in the fish food is retained by the fish. Seventy percent is digested and released as solid waste or excreted as ammonia via the gills or as urea (Timmons and Ebeling 2013). Total ammonia nitrogen (TAN) is comprised of two forms that exist in a ratio of un-ionized ammonia (NH~3~, which is toxic to fish) to ionized ammonia (NH~4~+ which in non-toxic).
· Kentucky State University6.3 pH
The pH is a measure of the acidity or basicity of a solution. It is determined by the presence or absence of free hydrogen ions (H^+^), where the more H^+^ present, the more acidic a solution is. An acidic solution has a low pH. The pH is measured on a scale from 1-14, with 7 being neutral. A pH value below 7 indicates a solution is acidic and above 7 indicates a solution is basic.
· Kentucky State University6.2 Temperature
Water temperature is more important in aquaponics than air temperature. Many water chemistry factors are affected by temperature, such as the amount of toxic ammonia (un-ionized) present and the solubility of oxygen. It also directly impacts the health and survival of both fish and plants. Fish are poikilothermic, or cold-blooded. This means that their body temperature is dependent on water temperature. At extreme temperature, fish will stop eating, becoming lethargic and susceptible to disease.
· Kentucky State University6.1 Dissolved Oxygen
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.
· Kentucky State University