One thing to consider, is that having higher than normal calcium levels, either means your specific gravity is going to be off, OR you are displacing some other ion in the seawater chemical soup. Some of the older folks here may remember the B-Ionic discussion a couple of years ago, in which MojoReef discussed the "Marble Chemistry" thing...Here's some of it as he posted over at R-V:
"Ok one more time, lol here is a simplier way of looking at your water chemistry. SW is made of of many different element, the total of all those elements is what makes your salinity. So if you salinity is at 35ppt (or 1.025-6) its telling you that you have 35000 element parts in your SW.
So view your SW as a bucket and your elements as marbles. Your bucket can hold only 35000 marbles if your salinity is 35ppt, no more or no less. Each marble is a different color and represents a different element. SO thier would be 10810 sodium marbles and 19500 chloride marbles and so on and so on. All of these elements that are in the bucket make up the buckets size. If you add more then what is the balanced ammount only tw things can happen. One is that your salinity (or bucket size) will increase or the other is that some marbles that are already in the bucket will come out and the salinity will be the same.
This is very important when trying to make sure you have the right level of elements in your tank. A lot of folks have thier levels set but do not take the salinity into the equation, and it is critical.Calcium, magnesium and alkalinity are of major concern to us and are the elements that get used the most in our tanks so let look at them.
At nsw salinity of 35ppt or 1.025-6 calcium is balanced at 415ppm, magnesium at 1290 and a alkalinity level of 2.5meq or 7-8dkh.
Now if you run your tank at a lower salinity the ammount of elelments the sw can hold will go down exponentically. So lets say some one runs their salinity at 1.023 or 30ppt. your bucket is smaller so you can only have 30000 marbles in it, all your elements in that bucket would be reduced by 14 %, so cal would be 354, mag would be 1101 and alk would be affected the same way. Each point you drop will reduce your element levels by 3.5 %.
So here is a example of a person that thinks thier fine but isnt.
They run thier salinity at 1.023 and has a calcium level of 450 and alk of 11. Now they might think hey 450 is a good number and the alk is in balance. But when you look at thier salinity level they are at the point of saturation and poisening. This persons level if thier salinity was 1.025-6 would be, calcium = 513 and alk at god knows what. So when your looking or the sweet spot make sure you base it on the salinity you have your tank on.
And for those that think elevated calcium levels are a good thing for corals, remember that calcium inhibits coral growth. And will eventually stress out and kill your corals."
