dosing for dummies

hello everyone... so I want do lower my calcium just a little bit. its arould 480...
would like to get it to 450. here is the question... my cal and alk dosing says i should use both cal and alk and dose the same amount every time. If i dose the same amount will both go up or down together? why would they say dose the same amount when i only want to adjust one slightly?
my readings are

cal 480
alk 9.0
mag 1380
phos .07 (working on that)
nitrates 0
nitrites 0
ph 8.4

I know these number are fine but my question is mainly why dose the same amount? how does it know which I am trying to adjust. currently I am using kalkwasser and wanted to dose alk and calcium using a dosing pump i just got