Alkalinity is the measure of the waters ability to buffer, right? Off to google...
...back with answers and a clearer picture (and info to share):
Q. What is the difference between water alkalinity and general hardness? Why do I need to test these parameters?
A. Alkalinity, often referred to as "carbonate hardness," or German carbonate hardness, is the measure of carbonate and bicarbonate concentrations in your aquarium water. Alkalinity is a measure of the ability of a solution to neutralize acid without changing the pH. It both controls and maintains water pH. Carbonate hardness is measured in degrees (dKH), parts per million of calcium carbonate (ppm CaCo3), or milliequivalents per liter (meq/L). You should perform regular tests for alkalinity, because a low alkalinity can allow water pH to fluctuate, and cause undue stress for aquarium inhabitants.
In contrast to carbonate hardness, general hardness is the measurement of the total dissolved minerals in your aquarium water. Test kits generally measure the amount of calcium and magnesium salts present, and the result is expressed in degrees dH or dGH. This parameter is not critical in most aquariums, except those containing fish and plants with special requirements. For example, depending upon the types of plants, a freshwater planted aquarium may require soft water with a low general hardness in the range of 3-5 dH. Conversely, an African Cichlid aquarium requires water with a higher general hardness range of 10-15 dH. Saltwater is not tested for general hardness because calcium and magnesium levels are tested separately. Common terms for water hardness are somewhat arbitrary, but generally fall within the dH ranges shown in the table.
Differences Between Water Alkalinity and Hardness
BTW: a buffer is a solution that contains either a weak acid and the base of that same acid, or a weak base and the acid of that same base. The purpose of a buffer is to keep the pH of the solution constant. Some buffers will keep the solution acidic, some neutral, and some basic. That's why you see chemical buffers for different pH ranges. The base part of the buffer will bind up a certain percentage of H+ ions that would otherwise cause the solution to become acidic (i.e. the pH would decrease). The acid part of the buffer will bind up a certain percentage of -OH ions that would otherwise cause the solution to become basic (i.e. the pH would increase).
A substance like crushed coral raises the pH by either absorbing H+ or releasing -OH (or maybe both). Same with peat or drift wood but they lower the pH by doing the opposite.
Thus having a high alkalinity is good because that means you have something in your water that is a good buffer and will absorb lots of ions that otherwise could quickly change your pH. For example: Ammonia is a base. In water, Ammonia steals one H from water to become Ammonium leaving an -OH behind. Thus, in an uncycled tank, as the ammonia builds up, the -OH concentration builds up, and the pH will rise too if the alkalinity of the water is low. If the alkalinity of the water is high, the buffer in the water is able to absorb a lot of the -OH ions and the pH can remain stable.
(I hope I didn't just totally confuse you!!!!)
