Panta, get some sulfuric acid (battery acid) and knock the pH down a little. You'll barely need any. 1-2ml will usually do about 50l.
You won't solve the pH issue with different types of water because water is almost always around 7 if it's for human consumption - distilled and RO will be similar if not dead on.
I fluffed my coir by filling a tub with far more water than it needed (coir floating or sunk), left for a few days (churning by hand occasionally), then rinse with pH corrected full strength feed. Squeezed all 75l to dry by hand, added maybe 30% perlite, fluffed. Very nice texture in the pots - it's so loose water will go straight down from the emitters, so it won't waterlog at all.
Feeding on Ionic Coir Grow
I also have some issues with yellowing. A quick feed tank check and my pH had bumped back up from 5.8 to 6.2. Reset. I have a datalogging .01 accurate pHmeter with software, so I might log the pH bouncing and make a pretty graph for the forum and other newbs to pH correction (like me).
I'm interested in the ca / mg / N deal, will have a read. Anyone find supplementing essential?
I also have mine infected with RootGrow mychorrhizal fungi - something you can't do so well with floods / constant flows / aeroponics