The Seachem Reef Advantage Calcium has other stuff in it, incl Mg and Sr, which maybe doesn't hold in mix as well. Just want to stress though, that the sediment/residue is very small, just enough that the last bit of liquid is not totally clear. And certainly not enough to be concerned about.
What I do like about this product, is that I never have to add Mg on its own. I test occasionally and it stays around 1400 - 1500, which is even on the high side.
http://www.seachem.com/Products/prod...dvCalcium.html