Briefly about carbon dioxide and pH
All natural waters contain some carbon dioxide. Pure water is an imperceptible conductor of electricity. In most cases, water is known as a non-ionized compound (not able to separate into positive and negative ions). The pH of pure water is equal to 7, which means a neutral environment. The pH of natural waters used in fish farming may be slightly acidic or slightly alkaline for various reasons. Almost alkaline waters are more suitable for fish breeding than acidic waters. Water whose range of pH changes from sunrise to sunset is between 6.5 and 9 results in optimal and fast growth of fish. Although Co2 is very soluble in water, it is a small component in the atmosphere. Less than 1% of carbon dioxide in water is in the form of carbonic acid and these components are difficult to separate.
H2o + co2 = H2co3
H2co3 = (H+) + (Co3 – -)
In pure water at a temperature of 25 degrees Celsius, the total concentration of carbon dioxide is about 48 mg/lit. At high concentrations of CO2, the pH decreases. At a carbon dioxide concentration equal to 30 mg/lit, the pH is about 4.8. Carbon dioxide should not cause the pH to drop below 4.5.
The pH of fish breeding ponds usually varies during the day due to photosynthesis and respiration. Because photosynthesis stops after sunset and all the plants and animals in the fish breeding pond consume oxygen, so the amount of dissolved oxygen in the water decreases. In pools with high fish density, the amount of CO2 from respiration may increase. This CO2 is combined with water and carbonic acid is formed and as a result the pH decreases.
The lethal points of acid and base (PH) for fish are around 4 and 11. However, if the waters become acidic less than 6.5 or their alkalinity becomes more than 9-9.5 and this happens for a long time, reproduction and growth in fish will stop (8).
PH problems are not uncommon in fish breeding ponds. In areas where there is a mine, seepage from the mine, which is acidic, causes the acidification of streams and lakes. Long-term acidification of lakes and streams will cause acid rain, which in turn has dangerous effects on fish populations in Europe and North America (7).
One of the main and important factors of changing the pH in swimming pools is the presence or absence of calcium compounds in their water. Calcium carbonate is one of the most abundant natural minerals that exists relatively pure or as particles in rocks and soil. This substance is relatively insoluble in pure water and only dissolves in water to the extent of 13 parts per million. Water saturated with calcium carbonate has a pH of about 9.3. Carbonates and bicarbonates can react with acids and bases and lead to a change in pH. By stabilizing pH at alkalinity of 6.5 or more, plant floaters improve their production capacity due to increased access to minerals (the amount of soluble phosphate). Alkalinity in the amount of 20 or more liters/mg traps CO2 and thus increases the amount of CO2 available for photosynthesis.
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This post is written by Bargonbad