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By Sascha W. Felix

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Application of lime of calcium carbonate (calcite) may not be suitable particularly when pond water attains seawater pH. Though agricultural lime may raise the soil pH, it will not be effective in maintaining suitable pH in the pond water. g. dolomite, mollusc shells or coral) which contain about 4 percent magnesium are more soluble at seawater pH and they could aid in maintaining optimum alkalinity and pH levels in the pond water (King, 1973). If the dikes are made up of acid sulfate soils, proper water management should be undertaken in order to reduce the problems associated with them.

Ammonia Chronic toxicity tests for ammonia were conducted with five species of penaeid shrimps viz. P. japonicus,P. occidentalis, P. schmitti, P. semisulcatus and P. setiferus. 45 mg NH3–N/l reduced growth by 50 percent of that of controls. 10 mg NH3–N/l. 10 mg unionized ammonia (NH3-N) per litre at selected temperatures, salinity and pH. 1 mg/l unionized ammonia nitrogen in water at a constant pressure of 1 atmosphere at different values of temperature, salinity and pH (Wickins, 1976) are as follows: From the table it can be seen that pH has a major effect, with the percentage of toxic unionized ammonia being much greater at high pH than at low pH.

5 can be managed only as long as frequent water changes are made. A change of water is required at least every three days. One way of improving ponds with acid sulfate soil is to repeatedly dry the pond and then flush it by repeatedly filling and draining. Acids formed by pyrite oxidation will gradually be removed by this process. After a pond is dug in an acid soil area, it should be flushed well until no, or little, red coloured scum from oxidized iron is observed. Lime should be added only after the pond is flushed.

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