It's a guarantee that you're not getting an accurate reading with that soil probe thingy. Just water them when they need it and stop worrying about the pH. You're not growing hydro. What soil are you using?
I water plants in soil with straight tap water all the time with no ill effects. I don't even bother with pH in soil.
This is where my waters at.
"Portland's water is currently treated to be at a pH of 8.2. The pH of Portland's water can vary by a small amount in the distribution system, but it generally ranges from about 7.4 to 8.4, with a median value of 7.8 to 8.1."
Any decent soil is going to have buffering agents. Trying to adjust soil pH based on a soil probe or runoff is a complete waste of time and can end up getting the soil chemistry all messed up. If you're using something to lower the pH and you keep putting it into your soil you can create problems when none existed before.