Ok, Agree with letting the tap water sit before using a liquid fresh dated test kit!
Also test for GH, more important then KH
I am in NY GH very low in the tap and it brings the PH down
I have to use corals in the HOB to keep the PH at 6.5
I do use the baking soda method also.
CC will keep your PH stable.
get the Gh reading then will know what is going on.
A large DW will bring down the PH, but not a lot.
Test your kit on a bottle of spring water and then the tap water.