1) ph LOW, ca LOW, dkh OK
use PH buffer + calcium additives
2) ph LOW, ca LOW, dkh HIGH
use PH buffer + calcium additives
3) ph LOW, ca OK, dkh OK
use PH buffer
4) ph LOW, ca OK, dkh HIGH
use PH buffer + a little calcium additive when it reduces
ca and dkh depletes together, so if both are alrite, or both are low, use only kalk solution to maintain them or boost them respectively.
kalk solution will help to maintain your PH so if all three are low use kalk solution to boost them....
note: do not alter them drastically, do it slowly over a few days....