Also make sure you test and balance alkalinity, calcium and magnesium. These are the three major components for proper reef chemistry stability. Links for more info on reef chemistry:
Aquarium System Volume Calculator:
http://home.comcast.net/~jdieck1/volcalc.html
The Reef Chemistry Calculator:
http://home.comcast.net/~jdieck1/chem_calc3.html
Reef Aquarium Water Parameters:
http://reefkeeping.com/issues/2004-05/rhf/index.htm
Magnesium in Reef Aquaria:
http://www.advancedaquarist.com/issues/oct2003/chem.htm
Solving Calcium and Alkalinity Problems:
http://www.advancedaquarist.com/issues/nov2002/chem.htm