Two thoughts I thought I'd throw out there.
First, if you have a buffering substrate such as ADA Amazonia or Fluval Plant and Shrimp, stop adding KH as the soil maintains a pH for you. You do need a small amount initially to cycle the tank, but after that, you don't want to add any more KH than you can help. This allows the soil to work longer.
Second, don't worry about pH at all - swings from CO2, changes from water change, etc. People have been dropping 1 full point in an hour every day for years with healthy fish. It's not the pH that's the issue, it's the KH. Unfortunately, all the crap we have in the hobby about pH is because we used to use pH as a proxy for KH since we didn't have KH test kits that were affordable. Having low KH is fine as long as you aren't trying to use a pH controller for CO2 injection. My dKH is always under 2 (in my non-buffering substrate tanks).