Stay away from Instant Ocean, Reef Crystals, and Tropic Marine if you want high CA levels, probably a couple others too. All of them test at about 340-360 right out of the box, and that is about the bare minimum you want in a reef. Though bringing a parameter up is much easier than decreasing it. The bottom line is all salts have short comings(ie low or high Ca, Alk, PH, magnesium, etc.), some are just more easily over come. There is no best salt, a search on any objective forum will prove that. This question comes up constantly. People have success w/ all of them. Best results are achieved by picking one that suits your needs and sticking/working with it.