alk calcium ph reactions to each other

[Bugzme]

how do these 3 items react to each other?
my tank readings are as follows ph=7.8, alk=3.5mgl, calcum is off the chart. i use sea-chem products.
i am aconstruction worker and would like this explained to me, i have read several articles but i don't understand
55 gallon, plenum filtration, small refugium, 3 maxijet 1200
thanks in advance
jeff

[Randy Holmes-Farley]

Calcium and carbonate will react with each other to form insoluble calcium carbonate (limestone) when mixed together.

In seawater, alkalinity is composed mostly of bicarbonate, and some carbonate. So some precipitation is always "trying" to happen.

As alkalinity rises, more carbonate is present, making it more likely that calcium carbonate will precipitate.

Also, as pH rises, the proportion of alkalinity present as carbonate rises, and the proportion present as bicarbonate declines. So as pH rises, precipitation of calcium carbonate is more likely.

Magnesium inhibits this precipitation, so lower than normal levels of magnesium can allow this precipitation to happen faster.

That's the nutshell version. :)