The calcium and alkalinity need to be in a proper ratio to each other, and balance is more important than the actual number they are at...within reason. Check the link in my signature for an easy read on the relationship between the different key elements.
Balanced calcium and alkalinity:
350 ppm to 1.4 dKH
375 ppm to 2.1 dKH
400 ppm to 5.6 dKH
425 ppm to 9.1 dKH
450 ppm to 12.6 dKH
475 ppm to 16.1 dKH