An alk of 7, while ok is really at the bottom of the scale of where it should be. Alk plays an important role in calcium and ph of the tank. When you have an Alk of 7 your balanced Ca should be around 400 or so. If you are running sps you would want to be 420 or plus. While the goal is not chasing numbers so much, we do want to get into the meat of a target range and than stay in that range, kind of like a strike zone in baseball (if that makes sense)
I am attaching an article that explains it way better than I could.