Sure thing.
kH is basically like a sponge. As your bio-filter converts ammonia on down to nitrAtes, nitric acids are produced and released into the water. Nitric acids are responsible for causing drops in pH if the kH isn't optimal. If the kH is optimal, the pH remains stable.
I like to look at kH as being the master of pH. The kH holds the pH on a short leash. Over time, nitrates (nitric acids) cause the leash to stretch out and allow the pH to wander further and further away from where it started.
If you were to start an aquarium with tankwater that has an excellent kH and pH and never did a single waterchange, the kH would drop and allow for the pH to drop as well. This is one of the most important reasons for waterchanges (besides nitrAtes). At every waterchange with water that has a good kH, you are effectively replacing any used up kH that is in the water and ensuring another week of nice, solid pH.
Heres a link that will explain this in detail. If you have any questions after reading this a couple times, don't hesitate to ask..........
pH, kH and their relationshipsDataguru (Betty) is much better at explaining these things than I am. Shes got a way with words that I seem to lack. Maybe she has a better way of explaining it.........
Hope this helps!