Ok, so have you given them a bunch of extra nutrients lately? If you have, then maybe do a flush, before you transplant. Reason being, is that after transplanting, you will still have a bunch of that old soil in there, and if you also gave them lots of additional nutrients, then it would be way to rich, and burn them/cause problems later.
I would probably just use the tap water if it were me, distilled if you want to be super safe maybe, but really I think the tap is fine.
I'm also happy to have folks that flush chime in, cause I've never had to. You are basically just giving a bunch of water to wash out all the extra nutes, IF you added a bunch.
I think you can forgo the peat moss with that fox farm, but maybe add some Perlite to it( about a 1/4 by volume, this adds a little extra oxygen capacity to the soil, which cannabis LOVES.
Just be real careful and gentle when you transplant, cradle that root zone from the top, with your fingers around the stalk, let the extra soil just fall off if no roots are into it yet. If you do flush, It will be easier to transplant if they dry out a bit after.
Once those plants get into that Fox Farm, you can kinda stop worrying about the PPM and PH a bit, since you will be growing in a living soil, with a community of micro organisims that take care of all that stuff for you. Nature figured that whole part out for us a long time ago. When you are growing in Hydro, coco, or using something besides soil, though, that's when it becomes your job to keep an eye on all that stuff.