Alkalinity and Hardness: Critical but Elusive Concepts in Aquaculture

Abstract

Total alkalinity and total hardness are familiar variables in aquatic animal production. Aquaculturists—both scientists and practitioners alike—have some understanding of the two variables and of methods for adjusting their concentrations. The chemistry and the biological effects of alkalinity and hardness, however, are more complex than generally realized or depicted in the aquaculture literature. Moreover, the discussions of alkalinity and hardness—alkalinity in particular—found in water chemistry texts are presented in a rigorous manner and without explanation of how the two variables relate to aquaculture. This review provides a thorough but less rigorous discussion of alkalinity and hardness specifically oriented toward aquaculture. Alkalinity and hardness are defined, their sources identified, and analytical methods explained. This is followed by a discussion of the roles of the two variables in aquaculture, including their relationships with carbon dioxide, pH, atmospheric pollution, ammonia, and other inorganic nitrogen compounds, phytoplankton communities, trace metals, animal physiology, and clay turbidity. Liming and other practices to manage alkalinity and hardness are explained. Changes in alkalinity and hardness concentrations that occur over time in aquaculture systems are discussed. Emphasis is placed on interactions among alkalinity, hardness, water quality, and aquacultural production.

Taxonomy of Means and Ends in Aquaculture Production—Part 4: The Mapping of Technical Solutions onto Multiple Treatment Functions

“…In ozonized systems, calcium carbonate has no effect on increasing alkalinity [22]. The dissolution of limestone is dependent on the dissolved CO 2 concentration [21]. Quicklime can be used to reduce the toxicity of copper [23] and cadmium [24] to fish.…”

“…Calcium hydroxide can also be used as a flocculant [20]. Limestone, which is most often a mixture of calcium carbonate and magnesium carbonate or dolomite, is a major source of alkalinity and hardness [21]. In ozonized systems, calcium carbonate has no effect on increasing alkalinity [22].…”

Taxonomy of Means and Ends in Aquaculture Production—Part 2: The Technical Solutions of Controlling Solids, Dissolved Gasses and pH

“…The relationship between pH and alkalinity requires careful monitoring and adjustment of both the alkalinity and CO 2 levels to maintain optimum pH [49]. For better understanding the concepts and the relationship between CO 2 , alkalinity and pH, further readings are recommended [48,51].…”

“…Furthermore, increasing the pH decreases the CO 2 concentration by shifting the carbonate carbon balance to bicarbonate and carbonate ions [50]. Adding or removing dissolved CO 2 affects the form of alkalinity, but it "does not affect overall alkalinity concentration" [51]. The relationship between pH and alkalinity requires careful monitoring and adjustment of both the alkalinity and CO 2 levels to maintain optimum pH [49].…”

A Gas Chromatographic Method for the Determination of Bicarbonate and Dissolved Gases

“…Alkalinity is usually reported in bicarbonate equivalents, since calcium and magnesium bicarbonates are usually the most important buffering agents in nature (Boyd et al, 2016). Bicarbonate is also important since it represents the largest pool of carbon dioxide in most waters (Raymond et al, 2008).…”