Ca Alk Mg and Ph all haves direct correlation. From my studies, keeping Ca over 450 is considered supersaturated. Balanced Ca at NSW alk 7dkh is about 390ppm. NSW is normally supersaturated at 450ppm. But the correlation is directly related to pH. When ph levels increase, the ability to retain levels of ca drops. At a higher ph calcium will precipitate more and more.
So if your Ca is above 450 and your ph is above 8.2 then your really wasting money because what your dosing is turning into calcium carbonate precipitation and THAT is helping to drive your alk up.
Just my .02
A really educational read on all of this can be found in the reefkeeping.com chemistry archives. It's title a "simplified understanding of the relationship between Ca, Mg, and Alk". Highly recommended read.
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