It depends on the atmospheric CO2 in my home. In the summer I have no problem keeping my pH in the 8.1-8.3 range with a window open. In the winter I go down to 7.8-8.1 and I use both a calcium reactor and a kalkwasser reactor. Start slow and measure your alkalinity weekly. Once you get the reactor dialed in you can be more lax.
A Guide to Using Calcium Reactors
http://reefkeeping.com/issues/2002-0...ture/index.php
Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm