Also, check your Magnesium levels. If it is low, it can be hard to balance alk/ca.
It would help to have more info on your tank (livestock, what and how much stony corals, coralline growth etc).
Also, if you have crazy coral growth (and a full tank of growing stony corals) you may have hit the limit for 2 part. I hit it with my 125 gallon and just took the jump to a Ca reactor.
- MikeT