I think the key to take out of RR's response is the "don't add anything you are not testing for"
for the calcuim there are a few ways of doing it. Guy mentioned B-ionic which is a two part additive that you do once per day to keep the peaks and valleys to a minimum. Another option is using a product like sea-chem's calcium additive. You add this once per week, but you will get bigger peaks and valleys (more in a sec on this). the last option, or option ill mention is one Guy said, the calcuim reactor. This is the most expensive out of the box, but will save money over then long haul.
My suggestion is this, if you do not have clams, or hard corals your calcuim usage isn't going to be all the quick so a product like sea chem's is going to work well as long as you test and make sure you are adding when you need to. If you have clams, hard corals you need to look at b-ionic or calcuim reactor for the bigger tanks.
Oddly enough, i have clams and my rate of calcium is pretty high when you add in the other users including the coralline and shrimp and snails. I use the b-ionic, but i also use the sea chem. i modified the sea chem to an every-other-day dose and my calcuim stays pretty high without going over board.
I like to keep my calcuim at 450-475, but others may take a 400-ish style.
just do it in stages as taking your calcuim from 300 to 450 overnight will not do you any favors at all.
just my 2 cents, or from the looks of the post, 5 cents
Indy