Hey Wendell,
Don't ask me about water chemistry, I'm just a saltwater hobbiest, not a scientist!
In all seriousness, I have only recently discovered that the calcium levels in my tank are WAY low. (First tested 2 months ago and was getting ~220ppm readings from my Salifert test kit).
I've never had problems with Alk levels though. I add Kent SuperBuffer dKH about once a week, and my Alkalinity is always 10.0-13.0dKH (3.5-4.5 meq/l) I have kept my Alk high over the past year in an effort to combat hair algae and a couple outbreaks of slime algae. Although I'm sure it was a combination of things, maintaining a high Alkalinity seemed to help with the battle and both hair algae and slime algae are non-existant in my tank now for the past 3 months.
So now (Well actually 2 months ago, as I got a Salifert test kit to replace my Seachem kit which I never really liked) I decided to start testing Ca levels because my newly acquired SPS seemed to be growing quite slow (the two M. Cap frags I got from you actually) and my 6 month old digitata wasn't growing as fast either. I was getting Ca readings of around 220ppm which surprised me as I have been dosing Kalk for makeup water for more than a year.
So I tried a bottle of Kent Liquid Reactor. Used the entire bottle over 10 days (dosed every night) and the Ca level went up a whopping 15ppm to 235ppm. So I chalk up that bottle of junk to experience, and acquired a container of Kent Turbo Calcium (which is what I wanted in the first place but the LFS didn't have it so I took the Liquid Reactor).
Been dosing Turbo Ca nightly for a week now, and Ca levels are now (tested today) at 300ppm. Instructions on the Turbo Ca mention that Alk levels are compromised with use of the product, so I have been twice-weekly adding SuperBuffer dKH instead of my usual once a week addition. Alk levels (tested today) are at 10.2 dKH (3.66 meq/l) measured with a Salifert test kit.
PS... I was lucky enough to borrow a Mg test kit (Salifert) from Troy, and my Mg level is at 1380ppm (tested 3 times over a week period). This is apparently well within reasonable parameters and seemingly not negatively affecting my Ca level (as it is steadily rising now).
So in summary (boy did I get off on a rant here).... I don't know how I am able to maintain such reasonable (even high) Alk levels over the past year even though my Ca levels were obviously receding except for the fact I regularily add small amounts of Kent SuperBuffer dKH every week or so to my tank?