Hey,
What salt are you using and what are you running your reef's salinity at?
Are you currently dosing? Daily? Or just when you need to get levels in range? (Important question) or just water changing?
Your a mixed reef right? (I forget what you said)
8 alk is ok for a mixed reef but theoretically your calcium should not be that high with an alk of 8.
What test kits are you using?
If your running an Sps tank and
If your not automatic dosing or running a calcium reactor you should raise that alk. With a mixed reef with sps or a Sps dominated tank you can easily swing into an unacceptable/unwanted range from additions or a simple growth spurt if your not ontop of testing or accurately understand your tanks consumption.
Personally if your dosing, stop dosing cal for a few days and continue with alk dosages until your cal comes down and your alk raises. try to shoot for the 9/430 or 10 / 450 range.
If you don't dose you can do a series of small water changes like mentions above said so you can obtain a better balance.