This is one of those painful subjects that can give you headaches for days. I like how Anthony Calfo puts it.
"Alkalinity and pH are distinctly different from each other, although their definitions and functions can be easily confused. For those of you as uninformed about water chemistry as I was when I first began, alkalinity is essentially a measurement of water's ability to neutralize acids. It is a measure of the buffering capacity of a system while pH is basically the measurement of the concentration of hydrogen ions in water, in terms of acidity or alkalinity. The alkalinity of water regarding pH issues merely refers to the basic end of a pH scale (alkaline) in contrast to the acidic end of the scale and does not reflect the buffering capacity of a system. It is easy to believe that water with alkaline pH is likely to be high in alkalinity (buffering capacity). However, this is not necessarily true. Water with a high pH, but a low alkalinity is regarded as unstable. Such water will quickly decline in pH with the natural accumulation of organic acids in aquarium systems.
The oldest and most common method of increasing the buffering capacity of salt water is the addition of sea buffer. Sea buffer is basically (no pun intended) a powdered mix of bicarbonates, carbonates, and borates. Such mixes are designed to increase the alkalinity (buffering capacity) of seawater without raising the pH beyond a set point. Some buffering products do raise the pH of seawater and should only be used with caution. Baking soda, sodium bicarbonate, is a significant portion of most dry mixes of sea buffer.
Anthony Calfo
If thats not enough to understand you then try to figure out just what your buffering with, and you have to tear apart your buffer to find out what percentage of bicarbonates, carbonates and borates it has. For instance in the case of using seachem as a buffer but you can't figure out why your corals are not growning, but you have perfect buffer, great dKH values going, only to find out that you have more borate than carbonates and the corals can't grow without the carbonates.
I'm going to stop now cause I feel like a nerve is pulsing in my head.
Thomas