Ok, if you've seen past reports I trust you, it's been a while since I lived in the area. Glad you're signed up for other alerts though.
The water change system sounds very neat, something I'd like to look into at the next house, not something I'm going to consider where we are.
I hadn't considered the pH swings when planning to add RO water for my South American tank. I'm assuming if I go 50/50 tap/RO I might be fine, but I'll have to do some research. I'll probably comment on my other thread so I don't derail yours.
I can imagine only doing one water change per week is much better than 4x you previously mentioned. I'm sure it's great for the discus too, especially if they're still maturing.