Water changes and corals using it. The few I have are growing and therefore consuming it. My tank is using more calcium than alkalinity, so, I am keeping my Calcium at 440ish and letting my Alk come down by itself. It's down to 9.5 now, would like to see it around 7-8. Not to sidetrack your thread, but, can anyone explain how Calcium drops whereas my Alk drops, but at a much slower rate.....