Interactions of pH, carbon dioxide, alkalinity and hardness in fishponds. Southern Regional Aquaculture Center publication no. 464. Liming Fishponds 3

• Main Authors: William A. Wurts, Robert M. Durborow
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1992
• Subjects: Alka; Carbonic acid
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.495.9840; http://www.aces.edu/dept/fisheries/aquaculture/pdf/464fs.pdf

Water quality in fish ponds is af-fected by the interactions of sev-eral chemical components. Carbon dioxide, pH, alkalinity and hard-ness are interrelated and can have profound effects on pond produc-tivity, the level of stress and fish health, oxygen availability and the toxicity of ammonia as well as that of certain metals. Most features of water quality are not constant. Carbon dioxide and pH concentra-tions fluctuate or cycle daily. Alka-linity and hardness are relatively stable but can change over time, usually weeks to months, depend-ing on the pH or mineral content of watershed and bottom soils. pH and carbon dioxide The measure which indicates whether water is acidic or basic is known as pH. More precisely, pH indicates the hydrogen ion concen-tration in water and is defined as the negative logarithm of the molar hydrogen ion concentration (-log [H+]). Water is considered acidic when pH is below 7 and basic when pH is above 7. Most pH values encountered fall be-tween O and 14. The recom-mended pH range for aquaculture is 6.5 to 9.0 (Figure 1). Fish and other vertebrates have an average blood pH of 7.4. Fish * Kentucky State University blood comes into close contact with water (1- or 2-cell separation) as it passes through the blood ves-sels of the gills and skin. A desir-able range for pond water pH would be close to that of fish blood (i.e., 7.0 to 8.0). Fish may be-come stressed and die if the pH drops below 5 (e.g., acidic runoff) or rises above 10 (e.g., low alkalin-ity combined with intense photo-synthesis by dense algal blooms – phytoplankton or filamentous algae). Pond pH varies throughout the day due to respiration and photo-synthesis. After sunset, dissolved oxygen (DO) concentrations de-cline as photosynthesis stops and all plants and animals in the pond consume oxygen (respiration). In heavily stocked fish ponds, carbon dioxide (CO2) concentrations can become high as a result of respira-tion. The free CO2 released during respiration reacts with water, pro-ducing carbonic acid (H2CO3), and pH ...