Hey scottie. Sunshine #4 is a good mix... it's what I use to grow all my plants. It does have dolomitic limestone which raises the PH of the medium.
I knew exactly what you meant by natural, I just mentioned how easily the PH of (non-PH'd) RO water changes. Always a good idea to add PH up and then PH down (or vice-versa) to RO water since this will help stabilize the PH.
I'm surprised you were able to take a reading of your (non-PH'd) RO water without thinking your meter was going crazy! My digital meter goes insane whenever I do this, even after just being calibrated. Goes all the way up to 8.6, just to go back down to 6.2, and never seems to settle.
RO water is extremely pure... 1 ppm in your case! That's basically DI water, and it was devoid of all minerals. I would add that Cal/Mag thing to all of your waterings and raise the PPM to about 50ppm. The GH products are very good. That limestone in the mix also adds Mag overtime, so you have to read your plants and act accordingly. I'll be following along.
Oh, and next time sign the +rep with your user name so that the person who receives it knows who it was from