Can somebody explain this Ca/Alk puzzle plz?

[fresh]

Hi all,

My tank has been setup and running for two months now. It is a 72gal tank with 100+ lbs of lr, and a 4"+ aragonite dsp. I have 500W of light running on the system (mh and pc).

I used IO salt to fill up the tank and then did a 5gal water-change about a month ago.

I just did a test on Ca and Alk (using salifert test-kits) and the puzzle is, my Ca reads 410 and my dkh reads 8.3!!!

I have a couple of corals that probably are consuming Calcium such as:
Moon coral
Candy Cane
Branching Hammer
Elegance
xenia
gsp
finger leather
sebea Anemone
and I just purchased a bleaching Acro (trying to revive it) and a a small cap frag.

Now from what I understood from all of you is that IO doesn't have that much Ca in it to start with, and overtime, Ca should go down as animals consume it.

I haven't added anything in terms of additives. Could this high Ca and Alk levels be due to the aragonite sand-bed?

Can somebody explain as I am very confused???

I was just about to dose the 2 part home-made Calcium-Chloride and Baking-soda right after my test showed me that I was on the low side, but after these results, I guess I will have to wait, correct???

What should I do? Should I still dose the 2 part additive, or should I just keep monitoring?

Thanks in advance.
fresh.