Hi bro, I am not sure whether this is the correct way, but u can try to set the ph to be 6.5. test the CA lvl before the CR kick in and after the CR stopped running, if the lvl of CA is with in the range then it should be good. If not then u will need adjust the ph again either up or down.
I think for CR there is a way to control the KH also,but need to wait for other more exp bro to input their advice. KH is a lot more important then CA when u are talking about SPS, so KH must always get it right. Cheer. =)