Thanks for the replies, everyone. Here's the info I can give about the tank parameters.
Tank:
Size - 75 gallons
Live Rock - at least 100 lbs. You can see the whole set up here:
http://billhenderson.org/images/fish...1190240584.jpg
Live sand bed, couple inches deep
Salinity - generally right around 1.025
Temperature - usually around 77 F in the morning, gets up to about 81 when the lights have been on all day
Filtration:
Fluval 404 (I am not sure what it's rated for flow, but the internet seems to indicate about 317 gph)
Rena XP3 (the box claims 187 gph)
Both filters contain carbon bags, chemi-pure, and polyfill. The Fluval also has ceramic rings the top chamber.
Lighting:
2x Coralife 20,000k - F20-T12-BP
1x Coralife Actinic - F18-T8-BP
1x Coralife Actinic 03 - F20-T12-BP
The lights are set on a timer. Both sets are on about 8-10 hours a day with overlap (about 12 hours of light total).
Unfortunately I don't have any kind of calcium test kit. Hopefully this can give us some clues, and if I have time this afternoon I'll get up the other water parameter numbers but unfortunately I have to head out now.
Again, thanks so much to everyone who is willing to help! I really appreciate it.