Easy to read article here...
http://www.chelonia.org/Articles/waterchemistry.htm
I use crushed coral in my filters but my KH is much lower than yours to start..
Technically if you maintain a good water change schedule, which replaces the KH consummed in your tank by biological processes...You should not have a problem with these values... Just monitor your KH and pH and plot it against the amount of water changes you do and you'll come up with the value that is optimum for maintaining your KH and pH
Hth,
al