Any thoughts on RO water
is it even worth the trouble
As far as for cuttings, I'm sure it wouldn't hurt the process. The tap water I have is very clean and very very low amounts of chlorides due to the town water being used a lot for food prodiction.
I don't think much calcium is necessary for initial root propigation. If you really want to know. Get several jars, and use plain RO water as the control. Then separate jars for variables, for example; one with tap, one with ro kelp, one tap and kelp, one with ro cal mag, one tap cal mag, one ro kelp
calmag and so on like that.
I would probably use powdered oyster shell or sea shell for water soluble calcium and epsoms for mag.
This isn't the easiest way to determine which method works, but it will be best way to gather data necessary to your individual circumstances.