Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
GH is not going to alter the pH.
Raising the KH will usually raise the pH.
1 teaspoon of GH booster is not very much, so I am not surprised the test did not pick it up. Try twice that much next time. Or read the label, and add enough to change the GH by 1 degree or maybe just a bit more.
If 4 teaspoons of baking soda changed the KH by 3 degrees, perhaps try half that, next time.
If the GH and KH drop off through the week, then adding some GH Booster and baking soda mid week should keep it stable.
A change of 2-3 degrees over a week is not much, but that much when you do a water change and the tank already very low is quite a bit, so yes, I would add some mid week.