Mojo is right....
the correct Ca
level is a function of salinity. Salinity, put VERY simply, is a measurement of the amount of certain minerals present in an H2O solution, the common measurement being in PPT.
Within this measurement, there are many different elements and compounds, all exisitng in a "balance" with one another. This balance is very similar throughout the ocean, reguardless of variences in salinity.
Most reefs average 35 ppt
salintiy...but this varies from 33 to 37 ppt
depending on the area, season, tides, ect. As salinity rises and falls, so do the levels of individual elements and compounds. But these elements and compounds still maintain a basic balance.
has an average Ca
level of around 380ppm.
Two reasons you see higher levels recommended. Increased coral growth and a Ca
"buffer zone" to compensate for Ca
depletion. There are however risks with running higher Ca
....namely chemical imbalances in the tank. Any parameter that rises above the average has the potential to create an imbalance.
you are better off trying to keep your levels balanced based on SG
than trying to simply shoot for a specific number. Balance is the key....