– Alkalinity is the ability to buffer the pH of water. The amount of base present in water is the total alkalinity. Common bases in aquaculture ponds are Carbonate, Bicarbonate, Hydroxyte, Phosphates and Berates. Carbonate (CO32-) and Bicarbonate (HCO3-) are the two most common bases and major constituents of alkali. Total alkalinity is measured in mg / L CaCO3 and the appropriate value for aquaculture animals is 75 to 200 mg / L CaCO3.
Water Quality Control – Carbonate-Bicarbonate Control in Surface Water or Well Water is formed by the interaction of CO2, lime and water while rainfall is mostly acidic due to exposure to carbon dioxide (CO2). Air so rain water causes the pH of the pond to drop.
– The nature of well water sources is also high in carbon dioxide (CO2), but low pH and dissolved oxygen are due to the microbial activity of the soil, but the formation of rocks in calcareous soils (CaCO3) or dolomite limestone, CO2 will dissolve limestone to release calcium and magnesium bicarbonate salt, resulting in some wells with high alkalinity, high pH and high hardness.
– Relatively high alkaline water source is good water buffering capacity because there are many bases to neutralize acid. CO2 is the main source of acid in the pond as the pH decreases, so that when the alkalinity is high, it is possible to neutralize the CO2. CO 2, pH and alkalinity are closely related, so that the pH of the water sample is less error-prone when performing rapid measurements within 30 minutes of water sampling.
– High alkalinity leads to high buffering and maintaining high pH, which helps to stabilize microalgae in the pond because the higher the alkalinity, the more soluble the phosphorus in water is the nutrient source for algae. Development.
– When high alkalinity, the ability to capture CO2 as well so they increase the photosynthesis of algae – when photosynthesis, algae using CO2 should increase pH, in addition algae and some plants are capable Combining Bicarbonate (HCO3-) to remove CO2 for their photosynthesis and releasing CO32- and releasing Carbonate from Bicarbonate by plants makes the water pH rise dramatically for fish and shrimp when the process Excessive photosynthesis
– Bicarbonate pH increase occurs for low alkaline water sources or high bicarbonate alkaline water (with low hardness). High bicarbonate alkalinity in soft water is usually caused by salt. Carbonate potassium or sodium carbonate are more soluble salts than calcium carbonate and magnesium carbonate salts.
Water hardness is important for aquaculture and is an important element of water quality. Unlike alkalinity, hardness is measured by the amount of divalent ion. Hardness is a mixture of divalent salts, but calcium and magnesium are the main sources of divalent ion of hardness. Hardness is also measured in mg / L CaCO3, which is easily misleading with alkalinity. – If limestone is a source of hardness and alkalinity, the hardness and alkalinity are usually the same, but in high alkaline water sources, because of the low hardness of bicarbonate (NaHCO3).
Calcium and magnesium are two important and important ions for shrimp and fish in the process of bone formation, scaling and some metabolic processes. The presence of calcium free ion in water also helps prevent the loss of sodium and potassium salts from the cell membrane in the fish body. Free calcium is recommended for fish ponds from 25 to 100 mg / L (equivalent to 63 to 250 mg / L CaCO3 of hardness), some other species of freshwater fish (strip bass, crawfish) require free calcium 40 to 100 mg / L (equivalent to 100 to 250 mg / L CaCO3 hardness).
3. Some notes
When the pH is higher than 8.3, the lime is insoluble in this high pH, so calcium sulfate (CaSO4) or calcium chloride (CaCl2) should be used to increase the hardness of the calcium at pH> 8.3.
Alkalinity stabilizes the pH so it increases toxicity to ammonia because at high pH most ammonia exist in NH3 form while high hardness does not affect ammonia toxicity.
– Metals like copper and zinc dissolve when the environment is acidic so high alkalinity will reduce metal toxicity. Calcium and magnesium ions also block metals so high hardness also reduces metal toxicity. Water for shrimp and fish should have an alkalinity of 75 to 200 mg / L and a hardness of 100 to 250 mg / L CaCO3.