There's a highly technical paper on exactly what Alkalinity is here: http://www.advancedaquarist.com/2002/2/chemistry, but for lay people (me), Alkalinity is basically a measure of how hard/easy it is to move a solution's pH. So if your Alkalinity is within the proper range, your pH should be relatively stable. If it's not, then your pH will move around quite a bit. Keep in mind, however, that in reality, your water's pH will be lowest when your lights are off, and highest when your lights are on, which is normal, so don't expect your pH to just stay at a certain number.
You can certainly do tests for pH, but I find that it is much more useful to test for alkalinity. Everytime I've checked for pH, it's always around 8.2 (that rose wine type color), which is why I don't bother to check it anymore.
As bimmerzs mentioned, hold off on the buffers and have your water tested. Specifically, test your alkalinity level. If it's not right, then spend your energy getting that right (it's easy), and most likely, you will need to bring it up (rather than down) which is very easy to deal with. Post your numbers back here and we'll guide you in the right direction for next steps. Resist the urge to dump stuff in your tank that the LFS recommends.
Also, do you have a skimmer? And what powerheads do you have? These will be your main aerating devices and are also very important in maintaining pH.
 and I would recommend some pickling lime (Kalkwasser) for raising the PH instead of using the "expensive" stuff your using. [smilie=wink.gif]
Here's a link for some info on kalk&id=0){kind=link}