I am a salty guy too and I use RO DI for that. What perhaps you did not realize is that your salt mix has more then salt. It has Carbonate and Bicarbonate which buffer the PH. As well as Calcium, Magnesium, Sodium, Potassium, Sulfate, and a whole mess of trace elements. Your RO water is no longer RO water but now sea water. We use RO water because it is like starting with a blank piece of paper and adding your list of things. If everyone started with different tap water...The salt manufacturer could not design a salt that would work out exactly the same for everyone. Trust me if you try to keep any fish in pure RO water it will die, you need to add a buffer, salt mix with a buffer in it, something.