While you're add it, I'd add this entire collection to your bookmarks:
http://archive.reefcentral.com/forums/showthread.php?s=&threadid=102605
Most of these articles will be a bit more than you need to know at this point, but I'm constantly going back to them. Some that I'd consider "must reads" would be:
Low PH: Causes and Cures
How to Select a Calcium and Alkalinity Supplementation Scheme
The “How To†Guide to Reef Aquarium Chemistry for Beginners, Part 2: What Chemicals Must be Supplemented
"good to read":
Nitrate in the Reef Aquarium
The “How To†Guide to Reef Aquarium Chemistry for Beginners,
Part 4: What Chemicals May Detrimentally Accumulate
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH
Solving Calcium and Alkalinity Problems
How to Select a Calcium and Alkalinity Supplementation Scheme
The Relationship Between Alkalinity and pH.