Just installed a new RO system

[ALToronto]

I agree about 5.5 being a good pH level for most orchids. I have some lithophytic paphs, however, so for them I save the runoff water from my aeroponic setup (pH around 8). I haven't had them long enough to see how they like it.

I plan to create a vertical "rock" wall for them (actually, my low-pH concrete - it's around 9, and similar to limestone) and give them regular acidic fertilizer solution - kind of like acid rain on limestone. I'll post it once I make it.