That's the right way to do it. Calcium is understood to be consumed and normally goes down overtime and so is alkalinity. Any of the two will not go up by itself. If you had dosed to raise your Alkalinity without the Part 2, your calc would have gone down some more. If you had dosed to raise calc without checking the other, your Alkalinity would have gone down some more. In short, make sure one of the 2 is on the upper level before dosing the other. If both are low then you have to compensate each other to reach the acceptable level. However before you do, it is very important that your magnesium is within 1300 ppm.