Sounds like you're using soil as simply a medium for adding ferts. I won't derail this nice thread beyond this post, but if the plant and microbes were allowed to control the soil, the pH measuring, deficiency conversations, etc all go away. Build the soil properly from the start, and most just add water. Maybe some castings as you go.
You can use RO water, which is essentially rain water
Again, sorry for the intrusion.