I find that in my tank, even with 15% weekly water changes, the alkalinity drops slightly every week. Not a whole lot, but I keep on top of it with weekly doses of Kent Superbuffer dKH. One tablespoon weekly keeps the alkalinity between 9 and 10. That's the only thing I dose with, but each tank is different. Best thing to do is start out with just water changes, check your levels weekly and go from there.