The following is a quote from http://www.seachem.com/ test kit that I purchased from my LFS. I hope this answers some of your questions
"Natural seawater has a total alkalinity of about 2.5 meq/L, of which about 0.1 – 0.2 meq/L is from borate. In an aquarium, it is advantageous for both pH control and improved calcium stability to have a higher borate content. This, however, should not be at the expense of carbonate. It is useful, then, to maintain a total alkalinity of about 4 – 5 meq/L with a borate component of about 1.5 – 2.0
meq/L."
Jim
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90 Gallon glass, 135#'s of rock and 2" sand. 2-250w 20k XM metal halides. 2-95 watt actinic VHO, 4 powerheads, Coralife skimmer. Maroon Gold Striped Clown, Blue Chromis, Kole Tang, Pygmy Angel, Serpent Star, Brittle Star,Gorgonians, Mushrooms, Yellow Polyps, Turbo Snails & Blue Legged Hermits. 20 gal sump with Caulerpa, Mag 7 return pump. | 
Carbonate Hardness Levels?? 
