Some of this is covered in the article on hardness and pH: http://www.tropicalfishkeeping.com/f...quarium-73276/
Unless you have a need to maintain a high pH, I would not bother with KH. I have near-zero KH in my tap water and I have in 20+ years never messed with it. I have soft acidic water fish, so this is fine.
Now, having said that, there are instances when we want to maintain a stable pH perhaps higher than what it may naturally fall to in a soft water tank. I have done this by using dolomite, just half a cup or less in the filter of a 100g tank will suffice.
Using a GH booster like Equilibrium--I can't remember if you have discussed this issue in another thread, i know there have been a couple members who have--does have some impact on pH I have discovered. My tanks are now remaining in the mid-6 range, whereas previously they were down around 5. And this is due to the Equilibrium I use to raise the GH from zero to 5 or 6 dGH.
KH has no direct effect on fish; it is simply a buffering agent for pH depending upon the level.
The use of baking soda (sodium bicarbonate) is not
advisable; this is explained in the article.