Having high alk can cause scaling issues over time. Take a look at the following thread for information about lowering alk.

http://www.poolforum.com/pf2/showthread.php?t=191

In regards to pH of 7.8 --- actually anywhere between 7.2-7.8 is fine. Some pools just naturally have a set point they seem to like to stay at pH-wise. But, in order to get the alk down, you'll need to lower the pH. It is all explained in the link above. If you have any questions after you read it, let us know.