Put the S. Boulardii on the shelf and stick with the Nystatin, you may not have to ever use it. You will nuke the Boulardii if you do at the same time as Nystatin.
The conventional salt is probably fine, but I have never used it myself
I cannot comment on the stool, candida can only be seen with a microscope but this seems to be common after anti-fungal enemas from what I've read.