Either the stuff I use must be pretty potent or I'm fortunate. 180-gallon tank, sps dominated, with a few large colonies. I dose 50ml of ALK per day and 40ml of Calcium per day. This keeps me in the range of 9alk and 420cal.
I also have been doing 15% partial water changes every week with a saltmix which is always 9-alk and 450-cal. Just the past weekend, I decided to start doing 15% every 2-weeks. Now that, I'm thinking about it, I should keep a close eye on these 2-parameters to see if they need to be adjusted with less PWC.