Jeremy, it's possible that the success calk is throwing off your alkalinity test. The way those tests work is there's a ph indicating dye and an acid. You put in the dye, then start titrating acid until the ph drops enough to change the color. If you have finely ground calcium carbonate, the acid will have to dissolve the calcium carbonate dust before it can really drop the ph, or something along those lines takes place. At least that's what Habib says, and if you ever tried to test the alk of water that's cloudy with SD dust, you'd come with a very high alk result; much higher than would actually be indicated by the presence of carbonate ions in the water. Alkalinity is really nothing more than the water's resistance to ph drops, not an actual PPM of carbonate ions. If your corals are doing well, great. But you might actually have significantly lower concentration of carbonate ions than your test shows.