To maintain the pH of the water to remain stable at around 6.8 it is necessary a chemical process that is expressed in alkalinity. Alkalinity is the ability estab-bufffer late of bicarbonate ions, carbonate and hydroxide ions in water. The third ion in the water will react with the hydrogen ions so as to reduce acidity or pH increase. Alkalinity is a quantity that indicates the content of bicarbonate ion (HCO3-) and carbonate (CO3 =) in the water.
1. The result of ionization of carbonic acid (H2CO3), when water saturated with CO2.
2. In addition, CO2 can react with the rocks also produce bicarbonate (HCO 3).
In water saturated with CO2, chemical equilibrium occurs as follows:
(A) H2O + CO2 <-> H2CO3 <-> H + + HCO 3
(B) 2HCO3ˉ <-> CO2 + H2O + CO3
(C) CO3 + H2O = <-> HCO 3 + OH
In water-containing calcium (CaCO3), the chemical equilibrium occurs as follows:
(A) CaCO3 + CO2 + H2O <-> Ca ++ + 2 HCO 3
(B) 2HCO3ˉ <-> CO2 + H2O + CO3 =
(C) Ca ++ + CO3 = <-> CaCO3
Alkalinity are usually expressed in ppm (mg / l) of calcium carbonate (CaCO3). According to Effendi (2000), the value associated with the type of water alkalinity. If water with alkalinity values of less than 40 mg / liter CaCO3 referred to as soft water (soft water). While the alkalinity waters more than 40 mg / liter CaCO3 called with water (hard water). Waters with high alkalinity values are more productive than the waters with low alkalinity value.
According Schimittou (1991) waters with low alkalinity. In general, a good environment for fish life is with a value above 20 ppm alkalinity. Bodies have the ability to maintain a stable pH to a certain extent that it can withstand changes in pH. The defense mechanism pH to various pH changes known as capacity-an estab-buffer pH.
Defense pH of the water to the changes made by the alkalinity of the process as follows:
CO2 + H2O <-> H2CO3 <-> H + + HCO 3 <-> CO3 = + 2H +
CO3 = (carbonate ion) in the chemical balance of the above, it is expressed as the alkalinity of the water.
While H + (ion H) is a source of acidity. The process of balance on a reversible reaction, meaning that the reaction can be run to the right (to produce H +) or to the left (producing CO2).
Therefore, when entered into the waters of the acid (H + ions), then H + will soon be bound by ion CO3 = move left and reaction produces CO2, (CO2 emitted into the air). At the time of the new acid is added, the pH will be measured is low, but after some time later, when the reaction began to move to the left, the pH will be moving back to the original numbers.
Thus when will require a lower pH in waters containing high chalk, will not be effective if it is only done by the addition of acid alone.
If only by the addition of acid only, the amount given should be in an amount more is to overcome the alkalinity first, as shown in the above reaction. Therefore it is necessary to lower the alkalinity first with boiling water or with water put through the peat. Meanwhile, to raise the alkalinity by adding calcium carbonate (CaCO3).