The disks failed. Twice. The first time they crumbled out of my silicone ice cube molds I thought "perhaps I didn't use enough water" so I tried again. No luck the second time either. So I have abandoned that project. Sometimes Internet tutorials just don't work out.
The bath fizzies, however, did just fine. They were more fun to make also because you get to use your hands to mix the ingredients and it felt nice. I've used one of the fizzies so far and it fizzes nicely, scented the bath nicely, and dissolved away nicely. I might acquire some cuter silicone molds and make some fizzies as gifts. I really want some more essential oils so I have different scents (particularly lavender) to experiment with.
So sometimes things work out and sometimes they don't.