What salt are you using? and what about buffers . . . . which are you using if any?
I have found that IO salt brings pH up nicely to 8.2. That and when combined with the correct buffer, it will stabilize there. Personally, I use seachem's powedered products for both alk and ca. Now, I dont know what the conversions are, but for alk I shoot for 3.43 meq/L with a ca of about 430ppm. I know these numbers are pretty exact, but thats just what seems to happen in my tank. I do get some flucuation, but not much.
HTH
Justin