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pH and pH Buffer|
As we mentioned in the FAQ section, pH is the most important element in your tank. Inappropriate pH level is reflected by the observation of your fishes becoming inactive and staying at the bottom of the tank most of the time. pH measures the acidic or basic reaction of the water. In pure water, there are Hydrogen (H+) and Hydroxide (OH-) ions. Pure water has a pH level of 7 which indicates the presence of equal amount of these two types of ions in the water. Natural sea water, however, is basic (or alkaline) and has a pH level of approximately 8.2. This means that there are more Hydroxide ions than Hydrogen ions in natural sea water. The carbon dioxide produced in the process of photosynthesis decreases the pH level in the water. Therefore, the pH levels are different in the "light" time (when your lights are on) and in the night time (when your lights are off).
pH Buffer as the Safety Device
pH buffer goes hand-in-hand with pH. Buffer capacity generally refers to the capability of the sea water to recover and stabilize to the level before any disruption. There are different types of buffer capability: pH buffer and KH buffer. (We will deal with KH buffer later.) The oxygen released in the photosynthesis is consumed by the living creatures in your tank and hence a balance between the oxygen and carbon dioxide levels is maintained. However, if the rate of photosynthesis is higher than the rate of respiration, then more carbon dixoide is produced. This drives the buffer capability down because the excess negatively charged ions are used up to counter-balance the acid produced by carbon dioxide molecules. If the buffer capability is exhausted, the excess carbon dioxide drives the pH level down quickly. Your tank can also lose its buffer capability from the acids released from the bacterial decomposition of the metabolic wastes in the water.
So the buffer capability acts as a safety device to absorb the constant changes of the pH level in the water. It restores the pH level as long as the capability is not exhausted. Once it is exhausted, the pH level in your tank will drop immediately and significantly within days. It is always critical to maintain the buffer capability in your tank at all time.
Maintaining your pH level
To maintain your pH level means to have the amount of basic ions to neutralize the excess acidic ions in the water. The neutralization requires negatively charged ions for the chemical reaction to happen. Among these negatively charged ions, carbonate (CO32-) and hydrogen carbonate (HCO3-) ions are generally termed as the carbonate hardness. Carbonate Hardness is a specific jargon to refer to only the concentration of the carbonate and hydrogen carbonate ions. That is, carbonate hardness excludes the hydroixde ions (OH-) completely.
As you may have already guessed, there is another type of buffer capability to describe the acid-neutralizing capability contributed by these two types of ions. This specific type of buffer capability is called KH buffer. This, however, is where some people get confused. What is the relationship between the pH and KH buffer? It sounds like both buffer capabilities referring to the same thing. We find it helpful to think of the KH buffer as a sub-set of pH buffer. This is because it is possible that your pH level is low and the KH level is high at the same time. The other contributing factor in the case of a decrease of pH level is the level of Calcium (Ca) ions. So there are two factors that contribute to the pH buffer capability in general: KH buffer and level of Calcium ions.
Maintaining your KH level
The KH-test is to measure the concentration of the carbonate and hydrogen carbonate ions in the water sample. Most KH-test kits include chemical solution for you to dip into the water sample. Count the number of droplets needed to turn the color of the water sample. Then calculate the concentration according to the instructions included in the test kit.
To maintain your KH-buffer capability means to add carbonate ions to replace the ones that were used up in previous neutralizations. One way of doing this is to add Calcium Carbonate (CaCO3). However, adding calcium carbonate directly has only a limited result. Calcium carbonate does not dissolve into the water quickly. It has been found that the dissolving process can be speeded up by passing carbon dioxide gas through solid calcium carbonate.
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