Just to make clear.....soil plants we use our well water. Hydro...RO or distilled only....ALWAYS.

But since your water IS so alkaline I think switching to RO or distilled will be your best answer. I use our well water for soil plants because it's already ph correct. If it wasn't.....say it was 8.5 like yours.....I'd lose it completely and go with RO or distilled.

Keep in mind that both those types of water have NO buffering ability. That's one reason they can be easily adjusted to your needs but it also means that until you stabilize your ph number it will jump around as well.